µ-LED, µ-LED DEVICE, DISPLAY AND METHOD FOR THE SAME

ABSTRACT

The invention relates to various aspects of a μ-LED or a μ-LED array for augmented reality or lighting applications, in particular in the automotive field. The μ-LED is characterized by particularly small dimensions in the range of a few μm.

This patent application is a continuation of U.S. patent applicationSer. No. 17/039,283 of Sep. 30, 2020, which claims the priorities of theGerman applications DE 10 2019 110 500.5 of 23 Apr. 2019, DE 10 2019 112490.5 of 13 May 2019, DE 10 2019 112 604.5 of 14 May 2019, DE 10 2019113 791.8 of 23 May 2019, DE 10 2019 125 875.8 of 25 Sep. 2019, DE 102019 121 672.9 of 12 Aug. 2019, DE 10 2019 113 768.3 of 23 May 2019, DE10 2019 114 442.6 of 29 May 2019, DE 10 2019 129 209.3 of 29 Oct. 2019,and DE 10 2019 130 866.6 of 15 Nov. 2019, the disclosure of which areincorporated herein by way of reference. Finally, this application alsoclaims priority from the PCT application PCT/EP 2020/052191 of 29 Jan.2020. The disclosure of PCT/EP 2020/052191 is incorporated herein byreference in its entirety. Additionally, this patent application isrelated to the following co-pending patent applications: U.S.application Ser. No. 17/038,283, entitled “μ-LED, μ-LED Device, Displayand Method for the Same,” filed Sep. 30, 2020; U.S. application Ser. No.17/039,097, entitled “μ-LED, μ-LED Device, Display and Method for theSame,” filed Sep. 30, 2020; U.S. application Ser. No. 17/039,422,entitled “μ-LED, μ-LED Device, Display and Method for the Same,” filedSep. 30, 2020; and U.S. application Ser. No. 17/039,482, entitled“μ-LED, μ-LED Device, Display and Method for the Same,” filed Sep. 30,2020.

BACKGROUND

The ongoing current developments within the Internet of Things and thefield of communication have opened the door for various new applicationsand concepts. For development, service and manufacturing purposes, theseconcepts and applications offer increased effectiveness and efficiency.

One aspect of new concepts is based on augmented or virtual reality. Ageneral definition of “augmented reality” is given by an “interactiveexperience of the real environment, whereby the objects from it, whichare in the real world, are augmented by computer generated perceptibleinformation”.

The information is mostly transported by visualization, but is notlimited to visual perception. Sometimes haptic or other sensoryperceptions can be used to expand reality. In the case of visualization,the superimposed sensory-visual information can be constructive, i.e.additional to the natural environment, or it can be destructive, forexample by obscuring parts of the natural environment. In someapplications, it is also possible to interact with the superimposedsensory information in one way or another. In this way, augmentedreality reinforces the ongoing perception of the user of the realenvironment.

In contrast, “virtual reality” completely replaces the real environmentof the user with an environment that is completely simulated. In otherwords, while in an augmented reality environment the user is able toperceive the real world at least partially, in a virtual reality theenvironment is completely simulated and may differ significantly fromreality.

Augmented Reality can be used to improve natural environmentalsituations, enriching the user's experience or supporting the user inperforming certain tasks. For example, a user may use a display withaugmented reality features to assist him in performing certain tasks.Because information about a real object is superimposed to provide cluesto the user, the user is supported with additional information, allowingthe user to act more quickly, safely and effectively duringmanufacturing, repair or other services. In the medical field, augmentedreality can be used to guide and support the doctor in diagnosing andtreating the patient. In development, an engineer may experience theresults of his experiments directly and can therefore evaluate theresults more easily. In the tourism or event industry, augmented realitycan provide a user with additional information about sights, history,and the like. Augmented Reality can support the learning of activitiesor tasks.

SUMMARY

In the following summary different aspects for μ-displays in theautomotive and augmented reality applications are explained. Thisincludes devices, displays, controls, process engineering methods andother aspects suitable for augmented reality and automotiveapplications. This includes aspects which are directed to lightgeneration by means of displays, indicators or similar. In addition,control circuits, power supplies and aspects of light extraction, lightguidance and focusing as well as applications of such devices are listedand explained by means of various examples.

Because of the various limitations and challenges posed by the smallsize of the light-generating components, a combination of the variousaspects is not only advantageous, but often necessary. For ease ofreference, this disclosure is divided into several sections with similartopics. However, this should exPlicitly not be understood to mean thatfeatures from one topic can not be combined with others. Rather, aspectsfrom different topics should be combined to create a display foraugmented reality or other applications or even in the automotivesector.

For considerations of the following solutions, some terms andexpressions should be explained in order to define a common and equalunderstanding. The terms listed are generally used with thisunderstanding in this document. In individual cases, however, there maybe deviations from the interpretation, whereby such deviation will bespecifically referred to.

“Active Matrix Display”

The term “active matrix display” was originally used for liquid crystaldisplays containing a matrix of thin film transistors that drive LCDpixels. Each individual pixel has a circuit with active components(usually transistors) and power supply connections. At present, however,this technology should not be limited to liquid crystals, but shouldalso be used in particular for driving μ-LEDs or μ-displays.

“Active Matrix Carrier Substrate”

“Active matrix carrier substrate” or “active matrix backplane” means adrive for light emitting diodes of a display with thin-film transistorcircuits. The circuits may be integrated into the backplane or mountedon it. The “active matrix carrier substrate” has one or more interfacecontacts, which form an electrical connection to a μ-LED displaystructure. An “active-matrix carrier substrate” can thus be part of anactive-matrix display or support it.

“Active Layer”

The active layer is referred to as the layer in an optoelectroniccomponent or light emitting diode in which charge carriers recombine. Inits simplest form, the active layer can be characterized by a region oftwo adjacent semiconductor layers of different conductivity type. Morecomplex active layers comprise quantum wells (see there), multi-quantumwells or other structures that have additional properties. Similarly,the structure and material systems can be used to adjust the band gap(see there) in the active layer, which determines the wave-length andthus the color of the light.

“Alvarez Lens Array”

With the use of Alvarez lens pairs, a beam path can be adapted to videoeyewear. An adjustment optic comprises an Alvarez lens arrangement, inparticular a rotatable version with a Moire lens arrangement. Here, thebeam deflection is determined by the first derivative of the respectivephase plate relief, which is approximated, for example, byz=ax2+by2+cx+dy+e for the transmission direction z and the transversedirections x and y, and by the offset of the two phase plates arrangedin pairs in the transverse directions x and y. For further designalternatives, swivelling prisms are provided in the adjustment optics.

“Augmented Reality (AR)”

This is an interactive experience of the real environment, where thesubject of the picking up is located in the real world and is enhancedby computer-generated perceptible information. Extended reality is thecomputer-aided extension of the perception of reality by means of thiscomputer-generated perceptible information. The information can addressall human sensory modalities. Often, however, augmented reality is onlyunderstood to be the visual representation of information, i.e. thesupplementation of images or videos with computer-generated additionalinformation or virtual objects by means of fade-in/overlay. Applicationsand explanations of the mode of operation of Augmented Reality can befound in the introduction and in the following in execution examples.

“Automotive.”

Automotive generally refers to the motor vehicle or automobile industry.This term should therefore cover this branch, but also all otherbranches of industry which include μ-displays or generally lightdisplays—with very high resolution and μ-LEDs.

“Bandgap”

Bandgap, also known as band gap or forbidden zone, is the energeticdistance between the valence band and conduction band of a solid-statebody. Its electrical and optical properties are largely determined bythe size of the band gap. The size of the band gap is usually specifiedin electron volts (eV). The band gap is thus also used to differentiatebetween metals, semiconductors and insulators. The band gap can beadapted, i.e. changed, by various measures such as spatial doping,deforming of the crystal lattice structure or by changing the materialsystems. Material systems with so-called direct band gap, i.e. where themaximum of the valence band and a minimum of the conduction band in thepulse space are superimposed, allow a recombination of electron-holepairs under emission of light.

“Bragg Grid”

Fibre Bragg gratings are special optical interference filters inscribedin optical fibres. Wavelengths that lie within the filter bandwidtharound AB are reflected. In the fiber core of an optical waveguide, aperiodic modulation of the refractive index is generated by means ofvarious methods. This creates areas with high and low refractive indexesthat reflect light of a certain wavelength (bandstop). The centerwavelength of the filter bandwidth in single-mode fibers results fromthe Bragg condition.

“Directionality”

Directionality is the term used to describe the radiation pattern of aμ-LED or other light-emitting device. A high directionality correspondsto a high directional radiation, or a small radiation cone. In general,the aim should be to obtain a high directional radiation so thatcrosstalk of light into adjacent pixels is avoided as far as possible.Accordingly, the light-emitting component has a different brightnessdepending on the viewing angle and thus differs from a Lambert emitter.

The directionality can be changed by mechanical measures or othermeasures, for example on the side intended for the emission. In additionto lenses and the like, this includes photonic crystals or pillarstructures (columnar structures) arranged on the emitting surface of apixelated array or on an arrangement of, in particular, μ-LEDs. Thesegenerate a virtual band gap that reduces or prevents the propagation ofa light vector along the emitting surface.

“Far Field”

The terms near field and far field describe spatial areas around acomponent emitting an electromagnetic wave, which differ in theircharacterization. Usually the space regions are divided into threeareas: reactive near field, transition field and far field. In the farfield, the electromagnetic wave propagates as a plane wave independentof the radiating element.

“Fly screen effect”

The Screen Door Effect (SDE) is a permanently visible image artefact indigital video projectors. The term fly screen effect describes theunwanted black space between the individual pixels or their projectedinformation, which is caused by technical reasons, and takes the form ofa fly screen. This distance is due to the construction, because betweenthe individual LCD segments run the conductor paths for control, wherelight is swallowed and therefore cannot hit the screen. If smalloptoelectronic lighting devices and especially μ-LEDs are used or if thedistance between individual light emitting diodes is too great, theresulting low packing density leads to possibly visible differencesbetween pointy illuminated and dark areas when viewing a single pixelarea. This so-called fly screen effect (screen door effect) isparticularly noticeable at a short viewing distance and thus especiallyin applications such as VR glasses. Sub-pixel structures are usuallyperceived and perceived as disturbing when the illumination differencewithin a pixel continues periodically across the matrix arrangement.Accordingly, the fly screen effect in automotive and augmented realityapplications should be avoided as far as possible.

“Flip Chip”

Flip-chip assembly is a process of assembly and connection technologyfor contacting unpackaged semiconductor chips by means of contact bumps,or short “bumps”. In flip-chip mounting, the chip is mounted directly,without any further connecting wires, with the active contacting sidedown—towards the substrate/circuit carrier—via the bumps. This resultsin particularly small package dimensions and short conductor lengths. Aflip-chip is thus in particular an electronic semiconductor componentcontacted on its rear side. The mounting may also require specialtransfer techniques, for example using an auxiliary carrier. Theradiation direction of a flip chip is then usually the side opposite thecontact surfaces.

“Flip-flop”

A flip-flop, often called a bi-stable flip-flop or bi-stable flip-flopelement, is an electronic circuit that has two stable states of theoutput signal. The current state depends not only on the input signalspresent at the moment, but also on the state that existed prior to thetime under consideration. A dependence on time does not exist, but onlyon events. Due to the bi-stability, the flip-flop can store a dataquantity of a single bit for an unlimited time. In contrast to othertypes of storage, however, power supply must be permanently guaranteed.The flip-flop, as the basic component of sequential circuits, is anindispensable component of digital technology and thus a fundamentalcomponent of many electronic circuits, from quartz watches tomicroprocessors. In particular, as an elementary one-bit memory, it isthe basic element of static memory components for computers. Somedesigns can use different types of flip-flops or other buffer circuitsto store state information. Their respective input and output signalsare digital, i.e. they alternate between logical “false” and logical“true”. These values are also known as “low” 0 and “high” 1.

“Head-up display”

The head-up display is a display system or projection device that allowsusers to maintain their head position or viewing direction by projectinginformation into their field of vision. The Head-up Display is anaugmented reality system. In some cases, a Head-Up Display has a sensorto determine the direction of vision or orientation in space.

“Horizontal Light Emitting Diode”

With horizontal LEDs, the electrical connections are on a common side ofthe LED. This is often the back of the LED facing away from the lightemission surface. Horizontal LEDs therefore have contacts that are onlyformed on one surface side.

“Interference Filter”

Interference filters are optical components that use the effect ofinterference to filter light according to frequency, i.e. color forvisible light.

“Collimation”

In optics, collimation refers to the parallel direction of divergentlight beams. The corresponding lens is called collimator or convergentlens. A collimated light beam contains a large proportion of parallelrays and is therefore minimally spread when it spreads. A use in thissense refers to the spreading of light emitted by a source. A collimatedbeam emitted from a surface has a strong dependence on the angle ofradiation. In other words, the radiance (power per unit of a fixed angleper unit of projected source area) of a collimated light source changeswith increasing angle. Light can be collimated by a number of methods,for example by using a special lens placed in front of the light source.Consequently, collimated light can also be considered as light with avery high directional dependence.

“Converter Material”

Converter material is a material, which is suitable for converting lightof a first wavelength into a second wavelength. The first wavelength isshorter than the second wavelength. This includes various stableinorganic as well as organic dyes and quantum dots. The convertermaterial can be applied and structured in various processes.

“Lambert Lamps”

For many applications, a so-called Lambertian radiation pattern isrequired. This means that a light-emitting surface ideally has a uniformradiation density over its area, resulting in a vertically circulardistribution of radiant intensity. Since the human eye only evaluatesthe luminance (luminance is the photometric equivalent of radiance),such a Lambertian material appears to be equally bright regardless ofthe direction of observation. Especially for curved and flexible displaysurfaces, this uniform, angle-independent brightness can be an importantquality factor that is sometimes difficult to achieve with currentlyavailable displays due to their design and LED technology.

LEDs and μ-LEDs resemble a Lambert spotlight and emit light in a largespatial angle. Depending on the application, further measures are takento improve the radiation characteristics or to achieve greaterdirectionality (see there).

“Conductivity Type”

The term “conductivity type” refers to the majority of (n- or p-) chargecarriers in a given semiconductor material. In other words, asemiconductor material that is n-doped is considered to be of n-typeconductivity. Accordingly, if a semiconductor material is n-type, thenit is n-doped. The term “active” region in a semiconductor refers to aborder region in a semiconductor between an n-doped layer and a p-dopedlayer. In this region, a radiative recombination of p- and n-type chargecarriers takes place. In some designs, the active region is stillstructured and includes, for example, quantum well or quantum dotstructures.

“Light Field Display”

Virtual retinal display (VNA) or light field display is referred to adisplay technology that draws a raster image directly onto the retina ofthe eye. The user gets the impression of a screen floating in front ofhim. A light field display can be provided in the form of glasses,whereby a raster image is projected directly onto the retina of a user'seye. In the virtual retina display, a direct retinal projection createsan image within the user's eye. The light field display is an augmentedreality system.

“Lithography” or “Photolithography”

Photolithography is one of the central methods of semiconductor andmicrosystem technology for the production of integrated circuits andother products. The image of a photomask is transferred onto aphotosensitive photoresist by means of exposure. Afterwards, the exposedareas of the photoresist are dissolved (alternatively, the unexposedareas can be dissolved if the photoresist is cured under light). Thiscreates a lithographic mask that allows further processing by chemicaland physical processes, such as applying material to the open areas oretching depressions in the open areas. Later, the remaining photoresistcan also be removed.

“μ-LED”

A μ-LED is an optoelectronic component whose edge lengths are less than70 μm, especially down to less than 20 μm, especially in the range of 1μm to 10 μm. Another range is between 10 to 30 μm This results in anarea of a few hundred μm² down to several tens of μm². For example, aμ-LED can comprise an area of about 60 μm² with an edge length of about8 μm. In some cases, a μ-LED has an edge length of 5 μm or less,resulting in a size of less than 30 μm². Typical heights of such μ-LEDsare, for example, in the range of 1.5 μm to 10 μm.

In addition to classic lighting applications, displays are the mainapplications for μ-LEDs. The μ-LEDs form pixels or subpixels and emitlight of a defined color. Due to their small pixel size and high densitywith a small pitch, μ-LEDs are suitable for small monolithic displaysfor AR applications, among other things.

Due to the above-mentioned very small size of a μ-LED, the productionand processing is significantly more difficult compared to previouslarger LEDs. The same applies to additional elements such as contacts,package, lenses etc. Some aspects that can be realized with largeroptoelectronic components cannot be produced with μ-LEDs or only in adifferent way. In this respect, a μ-LED is therefore significantlydifferent from a conventional LED, i.e. a light emitting device with anedge length of 200 μm or more.

“μ-LED Array”

See at μ-Display

“μ-display”

A μ-display or μ-LED array is a matrix with a plurality of pixelsarranged in defined rows and columns. With regard to its functionality,a μ-LED array often forms a matrix of μ-LEDs of the same type and color.Therefore, it rather provides a lighting surface. The purpose of aμ-display, on the other hand, is to transmit information, which oftenresults in the demand for different colors or an addressable control foreach individual pixel or subpixel. A μ-display can be made up of severalμ-LED arrays, which are arranged together on a backplane or othercarrier. Likewise, a μ-LED array can also form a μ-Display.

The size of each pixel is in the order of a few m, similar to μ-LEDs.Consequently, the overall dimension of a μ display with 1920*1080 pixelswith a μ-LED size of 5 μm per pixel and directly adjacent pixels is inthe order of a few 10 mm². In other words, a μ-display or μ-LED array isa small-sized arrangement, which is realized by means of μ-LEDs.

μ-displays or μ-LED arrays can be formed from the same, i.e. from onework piece. The μ-LEDs of the μ-LED array can be monolithic. Suchμ-displays or μ-LED arrays are called mono-lithic μ-LED arrays orμ-displays.

Alternatively, both assemblies can be formed by growing μ-LEDsindividually on a substrate and then arranging them individually or ingroups on a carrier at a desired distance from each other using aso-called Pick & Place process. Such μ-displays or μ-LED arrays arecalled non-monolithic. For non-monolithic μ-displays or μ-LED arrays,other distances between individual μ-LEDs are also possible. Thesedistances can be chosen flexibly depending on the application anddesign. Thus, such μ-displays or μ-LED arrays can also be calledpitch-expanded. In the case of pitch-expanded μ-displays or μ-LEDarrays, this means that the μ-LEDs are arranged at a greater distancethan on the growth substrate when transferred to a carrier. In anon-monolithic μ-display or μ-LED array, each individual pixel cancomprise a blue light-emitting μ-LED and a green light-emitting μ-LED aswell as a red light-emitting μ-LED.

To take advantage of different advantages of monolithic μ-LED arrays andnon-monolithic μ-LED arrays in a single module, monolithic μ-LED arrayscan be combined with non-monolithic μ-LED arrays in a μ-display. Thus,μ-displays can be used to realize different functions or applications.Such a display is called a hybrid display.

“μ-LED Nano Column”

A μ-LED nano column is generally a stack of semiconductor layers with anactive layer, thus forming a μ-LED. The μ-LED nano column has an edgelength smaller than the height of the column. For example, the edgelength of a μ-LED nanopillar is approximately 10 nm to 300 nm, while theheight of the device can be in the range of 200 nm to 1 μm or more.

“μ-rod”

μ-rod or Rod designates in particular a geometric structure, inparticular a rod or bar or generally a longitudinally extending, forexample cylindrical, structure. μ-rods are produced with spatialdimensions in the μm to nanometer range. Thus, nanorods are alsoincluded here.

“Nanorods”

In nanotechnology, nanorods are a design of nanoscale objects. Each oftheir dimensions is in the range of about 10 nm to 500 nm. They may besynthesized from metal or semiconducting materials. Aspect ratios(length divided by width) are 3 to 5. Nanorods are produced by directchemical synthesis. A combination of ligands acts as a shape controlagent and attaches to different facets of the nanorod with differentstrengths. This allows different shapes of the nanorod with differentgrowth rates to produce an elongated object. μ-LED nanopillars are suchnanorods.

“Miniature LED”

Their dimensions range from 100 μm to 750 μm, especially in the rangelarger than 150 μm.

“Moiré Effect” and “Moiré Lens Arrangement”

The moiré effect refers to an apparent coarse raster that is created byoverlaying regular, finer rasters. The resulting pattern, whoseappearance is similar to patterns resulting from interference, is aspecial case of the aliasing effect by sub-sampling. In the field ofsignal analysis, aliasing effects are errors that occur when the signalto be sampled contains frequency components that are higher than halfthe sampling frequency. In image processing and computer graphics,aliasing effects occur when images are scanned and result in patternsthat are not included in the original image. A moiré lens array is aspecial case of an Alvarez lens array.

“Monolithic Construction Element”

A monolithic construction element is a construction element made of onepiece. A typical such device is for example a monolithic pixel array,where the array is made of one piece and the μ-LEDs of the array aremanufactured together on one carrier.

“Optical Mode”

A mode is the description of certain temporally stationary properties ofa wave. The wave is described as the sum of different modes. The modesdiffer in the spatial distribution of the intensity. The shape of themodes is determined by the boundary conditions under which the wavepropagates. The analysis according to vibration modes can be applied toboth standing and continuous waves. For electromagnetic waves, such aslight, laser and radio waves, the following types of modes aredistinguished: TEM or transverse electromagnetic mode, TE or H modes, TMor E modes. TEM or transverse electromagnetic mode: Both the electricand the magnetic field components are always perpendicular to thedirection of propagation. This mode is only propagation-capable ifeither two conductors (equipotential surfaces) insulated from each otherare available, for example in a coaxial cable, or no electricalconductor is available, for example in gas lasers or optical fibers. TEor H modes: Only the electric field component is perpendicular to thedirection of propagation, while the magnetic field component is in thedirection of propagation. TM or E modes: Only the magnetic fieldcomponent is perpendicular to the propagation direction, while theelectric field component points in the propagation direction.

“Optoelectronic Device”

An optoelectronic component is a semiconductor body that generates lightby recombination of charge carriers during operation and emits it. Thelight generated can range from the infrared to the ultraviolet range,with the wavelength depending on various parameters, including thematerial system used and doping. An optoelectronic component is alsocalled a light emitting diode.

For the purpose of this disclosure, the term optoelectronic device oralso light-emitting device is used synonymously. A μ-LED (see there) isthus a special optoelectronic device with regard to its geometry. Indisplays, optoelectronic components are usually monolithic or asindividual components placed on a matrix.

“Passive Matrix Backplane” or “Passive Matrix Carrier Substrate”

A passive matrix display is a matrix display, in which the individualpixels are driven passively (without additional electronic components inthe individual pixels). A light emitting diode of a display can becontrolled by means of IC circuits. In contrast, displays with activepixels driven by transistors are referred to as active matrix displays.A passive matrix carrier substrate is part of a passive matrix displayand carries it.

“Photonic Crystal” or “Photonic Structure”

A photonic structure can be a photonic crystal, a quasi-periodic ordeterministically aperiodic photonic structure. The photonic structuregenerates a band structure for photons by a periodic variation of theoptical refractive index. This band structure can comprise a band gap ina certain frequency range. As a result, photons cannot propagate throughthe photonic structure in all spatial directions. In particular,propagation parallel to a surface is often blocked, but perpendicular toit is possible. In this way, the photonic structure or the photoniccrystal determines a propagation in a certain direction. It blocks orreduces this in one direction and thus generates a beam or a bundle ofrays of radiation directed as required into the room or radiation areaprovided for this purpose.

Photonic crystals are photonic structures occurring or created intransparent solids. Photonic crystals are not necessarilycrystalline—their name derives from analogous diffraction and reflectioneffects of X-rays in crystals due to their lattice constants. Thestructure dimensions are equal to or greater than a quarter of thecorresponding wavelength of the photons, i.e. they are in the range offractions of a μm to several μm. They are produced by classicallithography or also by self-organizing processes.

Similar or the same property of a photonic crystal can alternatively beproduced with non-periodic but nevertheless ordered structures. Suchstructures are especially quasiperiodic structures or deterministicallyaperiodic structures. These can be for example spiral photonicarrangements.

In particular, so-called two-dimensional photonic crystals are mentionedhere as examples, which exhibit a periodic variation of the opticalrefractive index in two mutually perpendicular spatial directions,especially in two spatial directions parallel to the light-emittingsurface and perpendicular to each other.

However, there are also one-dimensional photonic structures, especiallyone-dimensional photonic crystals. A one-dimensional photonic crystalexhibits a periodic variation of the refractive index along onedirection. This direction can be parallel to the light exit plane. Dueto the one-dimensional structure, a beam can be formed in a firstspatial direction. Thereby a photonic effect can be achieved alreadywith a few periods in the photonic structure. For example, the photonicstructure can be designed in such a way that the electromagneticradiation is at least approximately collimated with respect to the firstspatial direction. Thus, a collimated beam can be generated at leastwith respect to the first direction in space.

“Pixel”

Pixel, pixel, image cell or picture element refers to the individualcolor values of a digital raster graphic as well as the area elementsrequired to capture or display a color value in an image sensor orscreen with raster control. A pixel is thus an addressable element in adisplay device and comprises at least one light-emitting device. A pixelhas a certain size and adjacent pixels are separated by a defineddistance or pixel space. In displays, especially μ-displays, often three(or in case of additional redundancy several) subpixels of differentcolor are combined to one pixel.

“Planar Array”

A planar array is an essentially flat surface. It is often smooth andwithout protruding structures. Roughness of the surface is usually notdesired and does not have the desired functionality. A planar array isfor example a monolithic, planar array with several optoelectroniccomponents.

“Pulse Width Modulation”

Pulse width modulation or PWM is a type of modulation for driving acomponent, in particular a μ-LED. Here the PWM signal controls a switchthat is configured to switch a current through the respective μ-LED onand off so that the μ-LED either emits light or does not emit light.With the PWM, the output provides a square wave signal with a fixedfrequency f. The relative quantity of the switch-on time compared to theswitch-off time during each period T (=1/f) determines the brightness ofthe light emitted by the μ-LED. The longer the switch-on time, thebrighter the light.

“Quantum Well”

A quantum well or quantum well refers to a potential in a band structurein one or more semiconductor materials that restricts the freedom ofmovement of a particle in a spatial dimension (usually in thez-direction). As a result, only one planar region (x, y plane) can beoccupied by charge carriers. The width of the quantum well significantlydetermines the quantum mechanical states that the particles can assumeand leads to the formation of energy levels (sub-bands), i.e. theparticle can only assume discrete (potential) energy values.

“Recombination”

In general, a distinction is made between radiative and non-radiativerecombination. In the latter case, a photon is generated which can leavea component. A non-radiative recombination leads to the generation ofphonons, which heat a component. The ratio of radiative to non-radiativerecombination is a relevant parameter and depends, among other things,on the size of the component. In general, the smaller the component, thesmaller the ratio and non-radiative recombination increases in relationto radiative recombination.

“Refresh Time”

Refresh time is the time after which a cell of a display or similar mustbe rewritten so that it either does not lose the information or therefresh is predetermined by external circumstances.

“Die” or “Light-emitting Bbody”

A light-emitting body or also a die is a semiconductor structure whichis separated from a wafer after production on a wafer and which issuitable for generating light after an electrical contact duringoperation. In this context, a die is a semiconductor structure, whichcontains an active layer for light generation. The die is usuallyseparated after contacting, but can also be processed further in theform of arrays.

“Slot Antenna”

A slot antenna is a special type of antenna in which instead ofsurrounding a metallic structure in space with air (as a non-conductor),an interruption of a metallic structure (e.g. a metal plate, awaveguide, etc.) is provided. This interruption causes an emission of anelectromagnetic wave whose wavelength depends on the geometry of theinterruption. The interruption often follows the principle of thedipole, but can theoretically have any other geometry. A slot antennathus comprises a metallic structure with a cavity resonator having alength of the order of magnitude of wavelengths of visible light. Themetallic structure can be located in or surrounded by an insulatingmaterial. Usually, the metallic structure is earthed to set a certainpotential.

“Field of Vision”

Field of view (FOV) refers to the area in the field of view of anoptical device, a sun sensor, the image area of a camera (film orpicking up sensor) or a transparent display within which events orchanges can be perceived and recorded. In particular, a field of view isan area that can be seen by a human being without movement of the eyes.With reference to augmented reality and an apparent object placed infront of the eye, the field of view comprises the area indicated as anumber of degrees of the angle of vision during stable fixation of theeye.

“Subpixels”

A subpixel (approximately “subpixel”) describes the inner structure of apixel. In general, the term subpixel is associated with a higherresolution than can be expected from a single pixel. A pixel can alsoconsist of several smaller subpixels, each of which radiates a singlecolor. The overall color impression of a pixel is created by mixing theindividual subpixels. A subpixel is thus the smallest addressable unitin a display device. A subpixel also comprises a certain size that issmaller than the size of the pixel to which the subpixel is assigned.

“Vertical Light Emitting Diode”

In contrast to the horizontal LED, a vertical LED comprises oneelectrical connection on the front and one on the back of the

LED. One of the two sides also forms the light emission surface.Vertical LEDs thus comprise contacts that are formed towards twoopposite main surface sides. Accordingly, it is necessary to deposit anelectrically conductive but transparent material so that on the onehand, electrical contact is ensured and on the other hand, light canpass through.

“Virtual Reality”

Virtual reality, or VR for short, is the representation and simultaneousperception of reality and its physical properties in a real-timecomputer-generated, interactive virtual environment. A virtual realitycan completely replace the real environment of an operator with a fullysimulated environment.

In the following aspects of the Processing and methods for theproduction of a μ-LED or a μ-display or module are examined in moredetail. However, aspects of processing also include aspects relating tosemiconductor structures or materials and vice versa. In this respect,the following aspects can be combined with the many ideas and aspect ofμ-LED manufacturing or μ-LED devices themselves examples of such μ-LEDdevices can be found in WO application PCT/EP2020/052191, the disclosureof which is incorporated herein by reference in its entirety.

Due to the manufacturing process and the extremely small dimensions ofindividual optical elements, it can sometimes happen that individualpixel elements from the plurality of pixels in a display can bedefective. This problem has an increased impact on monolithic μ-displaymodules, since defects or variations in production lead very quickly tothe failure of a pixel due to its small size. If the defect densitybecomes too high, the entire module has to be replaced. Especially withmonolithic displays, individual defective pixels cannot be replaced.

Known solutions try to compensate for a failed pixel, for example, byadjusting surrounding or adjacent pixels to a higher luminosity andthereby at least partially compensating for the missing light of thedefective pixel. Since in many cases the replacement or repair of thesedefective pixels does not appear to be economically and procedurallysensible, it is desirable to be able to use a manufactured display withsufficiently good quality despite isolated defective pixels.

The aspects described below concerning Pixel elements with elec-tricallyseparated and optically coupled subpixels can compensate for such smalldefects so that an improved yield is achieved while maintaining thequality of the μ-displays or μ-display modules. These aspects are basedon the consideration to use measures suitable for the prevention ofoptical crosstalk. Therefore, the measures proposed in the following arenot only suitable for the above mentioned task, but a reduction ofoptical crosstalk has further advantages, if μ-LEDs are very close toeach other especially in monolithic components and a good opticalseparation should be achieved. In very densely packed monolithic arraysor μ-displays or μ-display modules, a clean optical separation betweenpixels is necessary to prevent the emitted light of a μ-LED fromradiating into an area of an adjacent pixel. To prevent opticalcrosstalk, trenches, or more generally, optically separating structuresare often provided between two μ-LEDs. While on the one hand opticalcrosstalk should be suppressed to achieve a sufficiently goodhigh-contrast image quality, the failure of a pixel may be morenoticeable.

Therefore, an optical pixel element is proposed to generate a pixel of adisplay, which is formed by at least two subpixels. According to anexample, 2, 4, 6, 9, 12 or 16 subpixels are provided per pixel element.In other words, a redundancy is created here, whereby the two subpixelsreceive the same driving information and are designed for the samewavelength, for example. So if one subpixel of these at least twosubpixels fails, the pixel element can still emit light at thiswavelength. According to an example, the luminosity of a subpixel can beadjusted to compensate for the missing light of a failed sub-pixel.According to an example, the subpixels are configured as so-calledfields. For example, if a pixel element is designed as a rectangularstructure, the subpixels within the structure of the pixel element areformed by a further subdivision into fields. Each of these subpixels ina field can be accessed independently of the subpixels in other fields.

The subpixels each have an optical emitter area. This is intended toensure that each subpixel can be individually controlled and functionindependently. The emitter region comprises a p-n junction, one or morequantum well structures or other active layers intended for lightgeneration. The emitter region is configured with a contact on itsunderside, which is intended for connection to a control unit or controlelectronics.

The control electronics is configured to control electrically theindividual pixel elements as well as the individual sub-pixels. Forexample, the drive electronics or the control unit may be configured todetect a defect in a subpixel and no longer use the defective subpixel.Furthermore, according to an example, the drive electronics can beconfigured to drive an adjacent subpixel in such a way that a luminosityis increased in such a way that a luminosity of an adjacent failedsubpixel is compensated. For this purpose, the control electronics canbe provided with a memory unit, for example, which stores an operatingstate of a subpixel. In other words, a central acquisition of subpixelsthat are detected as defective can take place in the memory, in order tocarry out defect compensation by luminosity adjustment or switching onor off of adjacent subpixels or pixel elements, if necessary. In anotherembodiment, for example, the time in which a subpixel is active can beincreased to compensate for a failed subpixel. If, on the other hand,all subpixels are functional, the control circuit can also control themall with reduced luminosity, reduced duration or even multiplexed. Usingfunctional subpixels with lower current and/or time duration mayincrease the lifetime of the subpixels.

To separate two adjacent subpixels within a pixel element from eachother, a subpixel separation element is provided. The sub-pixelseparating element has an electrically separating effect with regard tothe control of the respective emitter chips or the control of thesubpixels. In other words, this subpixel separating element can beconfigured in such a way that electrical interaction between the emitterchips of the adjacent subpixels is prevented.

Especially due to the use of semiconductors and the small distancesbetween the emitter areas of the individual subpixels in the [μm] range,the control of an emitter chip can have secondary electrical orelectromagnetic effects on spatially adjacent or surrounding areas.Under certain circumstances, this can lead to an adjacent emitter chipalso being activated when driving a primary emitter chip. The subpixelseparation element is therefore configured to prevent electricalcrosstalk or electrical crosstalk to the adjacent subpixel and possibleactivation of the adjacent subpixel.

On the other hand, the subpixel separation element should be designed tocouple optically the emitter chips of the neighbouring subpixels withrespect to the emitted light, so that the visual impression thatindividual subpixels are switched off is counteracted. By opticalcoupling is meant here that light generated by a primary emitter chip ora primary subpixel can cross over to the adjacent subpixel by opticalcrosstalk. This is an advantageous way to prevent a dark dot or darkspot from being created by the defect of a subpixel. Instead, light fromthe adjacent subpixel can pass over and be emitted in the direction ofemission from the defective subpixel. This is an advantageous way tocompensate for the visible effect of a defective subpixel. The subpixelseparating element therefore has no optical separating effect and shouldnot be achieved.

This is an advantage if a subpixel fails. Due to the lack of opticalseparation, the pixel is still perceived as a whole and there is nodifferent visual impression than when both subpixels are active. In oneaspect, the subpixel separation element can be designed in such a waythat it separates electrically but does not promote optical separationor even crosstalk. In one variant, the subpixel separating element isonly drawn up to just before the active layer of the two subpixels orinto the active layer. In other words, the subpixel separation elementelectrically separates two subpixel elements otherwise connected viacommon layers.

In one aspect, the subpixels have a common epitaxial layer. In manycases, pixel elements or entire displays are constructed in such a waythat a common layer or several superimposed layers are grown, connectinga large number of subpixels and/or pixel elements. This can also be usedto provide a common electrical contact or connection. According to anexample, the epitaxial layer has Group III elements gallium, indium oraluminum, and Group V elements nitrogen, arsenic or phosphorus, orcombinations thereof, or material systems with the mentioned elements.Among other things, this can influence the color and wavelength of theemitted light of a light emitting diode. The epitaxial layer can alsohave active semiconductor layers, e.g. a p-doped region and an n-dopedregion including the active interface regions.

For example, an emitter chip is arranged on a first side of theepitaxial layer transverse to a longitudinal extension of an epitaxiallayer plane. Its light is then emitted across the epitaxial layer in thedirection of a second opposite side of the epitaxial layer and radiatedfrom there. The subpixel separation element extends trench-like into theepitaxial layer across the epitaxial layer plane, starting from thefirst side of the epitaxial layer where the emitter chip or the μ-LED isarranged.

In other words, the subpixel separation element is implemented here as arecess, gap, slit or similar structure, which can also be filled with anelectrically insulating material. The insulating material should also beoptically transparent to facilitate optical crosstalk. According to anexample, the length of the trench is selected in such a way that drivesignals to a subpixel do not electrically cross over to a secondaryadjacent subpixel of the same pixel. Such a trench-like structureincreases, among other things, the electrical resistance due to thesignificantly longer path of the current flow, thus creating electricaldecoupling.

The optical effects that affect the emitted light, in turn, affect anarea of the epitaxial layer that is further in the middle or furthertowards the second far side of the epitaxial layer. Thus, the depth ofthe trench is chosen to ensure electrical decoupling, but on the otherhand, the trench ends before an area of the epitaxial layer where lightcan be transmitted between two adjacent subpixels. For example, theemitter chip's direction of emission runs across the epitaxial layer toallow light to exit at the opposite second side.

According to an example, the trench runs at a right angle relative tothe epitaxial layer plane. Assuming this course of the trench, anotherexample shows that a length d1 of the trench is smaller than an overallthickness of the epitaxial layer. It is assumed that the epitaxial layerhas at least approximately the same total thickness over a large numberof pixel elements and subpixels. According to another example, thelength d1 of the trench between the pixel elements is equal to thethickness of the epitaxial layer. In other words, the trench iscontinuous from the first side of the epitaxial layer to the second sideof the epitaxial layer. According to another example, the trench runscontinuously diagonally through the epitaxial layer at an angle between0 and 90° relative to the epitaxial layer plane.

In one aspect, each pixel element or its subpixel elements comprisesseveral semiconductor layers in the form of a layer sequence, with anactive layer for generating light. The active layer may comprise quantumwells or any other structure prepared to generate light. In an aspect,one or more layers extend over several pixels or subpixels. For example,the active layer may be intended to extend over several subpixels of acolor.

According to an aspect, the subpixels or pixel elements are electricallycontactable and/or controllable independently of each other. For thispurpose, for example, contacts can be provided on the side of thesubpixels that is remote from an epitaxial layer. These can bemechanical contacts, solder connections, clamp connections or similar.The decisive factor here is that the subpixels of the individualsubpixels can be contacted and electrically operated without significantinteraction with the adjacent subpixels of the adjacent subpixels. Thiscan be especially advantageous for detecting the functional or operatingstate of a subpixel, since diagnostic information can be generatedindividually for each subpixel. It is also useful to switch individualsubpixels on or off without including the adjacent subpixels. Thisreduces thermal or other stress on the subpixels at higher intensities,since several subpixels can be operated simultaneously at lowerintensities.

According to another aspect, the contacting of the individual subpixelstakes place via a carrier substrate. On the one hand, the carriersubstrate should provide mechanical stability and, on the other hand,integrate the fine conductor structures for the individual contacting ofthe individual sub-pixels. Other elements such as control electronics ordriver circuits can also be integrated in the carrier substrate andespecially in silicon wafers. This can have the same material system,but also a different material system via matching layers. In this way,silicon can also be used as a carrier material. This means that circuitsfor control in particular can be easily implemented in this carrier.

According to an example, a brightness of the pixel element can beadjusted by switching individual subpixels off or on. The advantage hereis that switching off or switching on alone can already provideeffective brightness control. This can, for example, significantlysimplify a control electronics or a control unit. According to anotherexample, the brightness of one or more subpixels of the pixel elementcan also be adjusted. Hereby a brightness can be adjusted or calibratedin even finer gradations, or a color spectrum can be adjusted orcalibrated more precisely in interaction with different wavelengths ofthe subpixels of the same pixel element. The brightness can be adjustedby PWM control. If a subpixel has failed, an equivalent brightness canstill be achieved by extending the PWM control accordingly. Conversely,if the subpixels are intact, the PWM drive can be adjusted, allowing thesubpixels to operate at their maximum efficiency and possibly alsoresulting in lower thermal stress and thus a longer lifetime.

If, for example, eight subpixels are structured in a pixel element, abrightness dynamic of 2^3 levels can be achieved without varying othercontrol variables such as current or on-time. In other words, a dynamicrange can be increased by a factor of 2^3 in this design variant. Thiscan also limit the complexity of the control electronics and thus thecorresponding costs.

In another aspect, a μ-display is proposed, which has a plurality ofpixel elements as described above and below. According to an aspect,such a μ-display can be an optical semiconductor display, e.g. forapplications in the augmented reality area or in the automotive sector,where small displays with very high resolutions are used. Such a displaycan also be used in portable devices such as smart watches or wearables.

A pixel element separation layer is provided between two adjacent pixelelements. This is configured in such a way that the adjacent pixelelements are electrically separated with respect to the control of therespective pixel elements. Furthermore, the pixel element separationlayer is configured in such a way that the light emitted by the pixelelements is optically separated. A pixel element separation layer caninitially be understood abstractly as any structure or material thatseparates two pixel elements from each other. Usually, a large number ofsuch pixel elements are arranged next to each other in one plane, forexample on a carrier surface, and are connected to control electronicsvia contacts. In this way, a display can be formed in its entirety.

The electrical and electromagnetic separation is intended to ensure thata pixel element can be driven independently of the adjacent adjacentpixel elements and that there is minimal or no electrical orelectromagnetic interaction, in particular no optical interaction. Thisis important for the sole purpose of being able to generate each pixelindependently of the others for displaying a specific image content onthe display. The optical separation in turn is necessary in order toachieve sufficient sharpness and contrast, or the ability to separatethe individual pixels from one another on the display.

In an aspect, several pixel elements have a common epitaxial layer. Thepixel element separation layer is trench-like and extends transverselyto the epitaxial layer plane in the emission direction of the emitterchips. In other words, the pixel element separation layer is adapted asa trench, slit, slot or similar recess, which either does not containany solid material or, for example, comprises a reflecting or absorbingmaterial. In one example, the pixel separation element is filled with aninsulating material in which a mirror layer is incorporated. Theinsulating material electrically separates two adjacent pixels and themirror element prevents optical crosstalk. In some embodiments, themirror element is also designed to collimate or support the light.

The pixel element separation layer is configured to prevent electricalor electromagnetic signals from being transmitted from one pixel elementto another pixel element. At the same time, the pixel element separationlayer should achieve that as little or no light as possible is emittedfrom one pixel element to an adjacent pixel element. In an example, thepixel element separation layer can be formed simply by placing twoseparated pixel elements next to each other when they are arranged,resulting in a corresponding insulating or reflective boundary layer.According to an example, the trench is perpendicular to the epitaxiallayer plane, and a length of the pixel element separation layer is lessthan or equal to the thickness of the epitaxial layer.

According to another aspect, the trench depth of the pixel elementseparation layer is greater than a trench depth of the subpixelseparation layer. This is supposed to offer the advantage that the pixelelement separation layer causes an electrical as well as an opticalseparation by its greater length. On the other hand, only an electricalseparation is achieved due to the smaller trench depth between thesubpixels, whereby optical crosstalk is definitely desired. In someaspects, the depth of the pixel element separation layer reaches throughthe active layer of second adjacent pixels and separates them. Inaddition, the pixel element separation layer can reach to the emittingsurface or just below.

In a further aspect, a procedure for calibrating a pixel element isproposed. This procedure is based on the idea that when a display is putinto operation an optimal control should be possible. This can mean, forexample, that defective subpixels are to be detected as such and then nofurther control is carried out. In this way, error messages ormalfunctions can be avoided. By building up the pixel elements with thesubpixels, it can be achieved that each subpixel can be individuallycontrolled and checked.

Therefore, in a first step a subpixel of a pixel element is controlled,for example by an electronic control unit or a control unit. The nextstep is the acquisition of defect information of a subpixel. In otherwords, the control electronics can be configured and adapted in such away that a malfunction or defect is detected. For this purpose, forexample, a current intensity can be measured or other electricalquantities can be evaluated.

In a further step, the defect information is stored in a memory unit ofthe control unit. This information can be used, for example, to optimisethe control by the control electronics. If, for example, a certainluminous intensity is to be achieved and it is known that a certainsubpixel is defective, the control electronics can control theneighbouring subpixels in a correspondingly differentiated manner, forexample to compensate for a luminous intensity. As a result, a quantityof light emitted by the pixel element would be exactly or nearlyunchanged despite a defective subpixel and would not be noticed by auser.

In a further aspect of the method, the control, acquisition and storageis carried out sequentially for all individual subpixels of a pixelelement. In other words, an electronic control unit can be configured insuch a way that it checks all available subpixels one after the othervia the individual separately addressable emitter chips and thus detectsa functional state of the entire pixel element. According to an example,this can be done once when a display is switched on or after a certainperiod of time.

An extension of pixelated or other emitters, where optical andelectrical crosstalk is reduced, is presented in the following concepts.

In conventional monolithic pixel arrays, it is common in some aspects toetch through the active zone in order to separate and address theindividual pixels individually. However, the etching process through theactive layer causes defects, which on the one hand can lead to,increased leakage currents at the edges and on the other hand produceadditional non-radiative recombination. As the pixels become smaller andsmaller, the relative damage area effectively increases. Conventionally,the edge of the etched active zone is passivated by various methods tosolve the problem. Such methods are regrowth, in-situ passivation,diffusion of species to shift the pn-junction and increase the band gaparound the active zone, and wet etch washing to remove the damage as faras possible.

Under the proposed principle, a pixel structure with a material bridge,which at least still includes the active layer. This reduces anincreased defect density in the area of the active layer.

Thus an array of optoelectronic pixels or subpixels, in particular amicropixel emitter array, a micropixel detector array, or a combinedmicropixel detector-emitter array, comprises a respective pixel orsubpixel forming an active zone between an n-doped layer and a p-dopedlayer. According to the proposed principle, between two adjacent formedpixels, material of the layer sequence from the n-doped side and fromthe p-doped side up to or in cladding layers or up to or at leastpartially into the active zone is interrupted or removed. In this waymaterial transitions with a maximum thickness dC are formed, wherebyelectrical and/or optical conductivities in the material transition arereduced.

According to a second aspect, a method for the production of an array ofoptoelectronic pixels or subpixels is proposed, in which in a first stepalong the array a whole-surface layer sequence with an n-doped layer anda p-doped layer is provided, between which an active zone suitable forlight emission is formed. Subsequently, between adjacent pixels to beformed, material of the layer sequence is removed from the n-doped sideand from the p-doped side up to or into undoped cladding layers or up toshortly before or to the active zone. The removal can be done by anetching process. After removal, however, a material transition remainsbetween the adjacent pixels, which comprises the active region andoptionally a small area above, below or from both sides. This comprisesa maximum thickness dC at which electrical and/or optical conductivityis effectively reduced by the material transition.

With the proposed concept, an array of pixels can be created over alarge area. Material is removed by the etching process, but a materialtransition remains between adjacent pixels or sub-pixels, whichencompasses the active layer. Thus, the etching process does notincrease the defect density in the area of the active layer, especiallyin the pixel areas. Nevertheless, the individual pixels or sub-pixelsare optically and electrically separated from each other. It istherefore proposed to manufacture micropixel emitter arrays andmicropixel detector arrays formed by micropixels without etching throughthe active zone in such a way that optical and electrical crosstalk aswell as performance and reliability losses of etched active zones areavoided. In this way, etching defects are avoided or their number iseffectively reduced.

In this context, pixel or subpixel each denotes a μ-LED that emits lightduring operation. As a rule, several subpixels of different colors arecombined into one pixel, also known as an image element.

According to one embodiment, the removed material can be at leastpartially replaced by a filler material. In other words, after thepartial removal of the material and especially the n- or p-doped layers,the space created is filled up again, resulting in a planar surface.This allows the functions of mechanical support, bonding and/orelectrical insulation to be provided.

According to a further embodiment, the removed material can be at leastpartially replaced by a material that has a relatively small band gapand thus absorbs light from the active zone. This effectively reducesoptical crosstalk. Alternatively, the removed material can be at leastpartially replaced with a material having a high refractive index, inparticular higher than the refractive index of one of the claddinglayers or the active zone. This can effectively create highly refractiveinterfaces that stop the propagation of fundamental modes. Furtheralternative light absorbing material and/or material with highrefractive index can be applied at a respective material transition inone aspect. Thus, the material influences a wave guide in the materialtransition and prevents crosstalk.

According to a further embodiment, the material with a high refractiveindex can be formed by diffusing or implanting a material increasing therefractive index into a filling material, in particular into arespective cladding layer. This allows the arrays to be easily andeffectively improved with respect to crosstalk without etching.

Another aspect concerns a reduction of electrical crosstalk. Accordingto this, a material for increasing light absorption and/or a materialfor increasing electrical resistance can be introduced into the activezone of a respective material transition. The corresponding proceduresare relatively simple to carry out. Thus, the arrays can be effectivelyimproved with respect to crosstalk in a simple way without etching.

According to a further embodiment, at least one optical structure, inparticular a photonic crystal and/or a Bragg mirror, can be generatedalong the material transitions, at or in these. These are particularlyeffective elements for reducing optical crosstalk. Such a photoniccrystal or structure can also be used to improve collimation of light.

In another aspect, an electrical bias can be applied to the two mainsurfaces of the material transitions by means of two opposite electricalcontacts and an electrical field can be generated by a respectivematerial transition. This is an effective element in reducing opticalcrosstalk. In this case, the electric field is generated by applying abias voltage. This bias voltage can, for example, be derived from ororiginate from the voltage for operating the pixels. However, in someaspects such a field can also be determined by an inherent materialproperty. In one aspect, for example, it is intended that an electricfield is generated by means of an n-doped material and/or p-dopedmaterial applied to or grown on at least one of the two main surfaces ofthe material transitions by a respective material transition. Electricfields are thus built into the corresponding array, whereby it is notnecessary to apply a voltage.

According to a further embodiment, the exposed main surfaces of thematerial transitions and/or exposed surface areas of the pixels can beelectrically insulated and passivated by means of a respectivepassivation layer, in particular one containing silicon dioxide. In thisway, current flow through selected areas of an array, in particularthrough the material transition acting as a waveguide, can beeffectively and selectively prevented. The main surfaces of the pixelscan be electrically contacted by means of contact layers, so that avertical optical component is thereby produced. One of the main surfacescan be electrically connected to each other via a shared layer.According to a further embodiment, the material and/or the materialtransitions between a pixel and its neighbouring pixels can be formeddifferently to each other, especially depending on the direction.

For the production of a μ-LED display, it seems to be useful to duringthe processing to provide subunits of μ-LEDs, and separate these to beable to process them further. In this way, the subunits can be testedindividually. If μ-LEDs in the subunits fail, it is not necessary toreplace the entire μ-display, but only the subunit. On the other hand,by adapting one process step, the production can be made more flexible,so that different sizes can be produced. This approach is particularlysuitable as a modular architecture for μ-LEDs.

According to an aspect of the modular architecture, a method formanufacturing μ-LED modules is proposed, with the steps

Creating at least one layer stack providing a base module on a carrier;

depositing of a first contact to a surface area of the layer stackfacing away from the carrier;

depositing of a second contact to a surface area of a first layer facingaway from the carrier.

Alternatively, the following steps can be taken:

Generating at least one layer stack providing a base module, comprisinga first layer formed on a carrier, on which an active transition layerand on which a second layer is formed;

opening a surface area of the first layer facing away from thesubstrate;

Connecting a first contact to a surface area of the second layer facingaway from the carrier;

Connecting a second contact to the surface area of the first layerfacing away from the carrier.

Accordingly, a μ-LED module then comprises at least one layer stackproviding a base module, having a first layer formed on a carrier, onwhich an active transition layer and on which a second layer is formed,a first contact being connected to a surface region of the second layerfacing away from the carrier, a second contact being connected to asurface region of the first layer facing away from the carrier.

In this way, a base module can be created as the basic component of aμ-LED module with, in particular, a contact level for the contacts. Thebase module is part of a larger system, but in its simplest form, it canin turn comprise a μ-LED. In one aspect, the base module containsseveral, at least two μ-LEDs. These can be controlled individually orcan be adapted as redundant forms. Thus, according to a building blockor modular principle, a whole can be divided into parts, which arecalled modules. With a rectangular or any other arbitrary shape and acommon function of light emission, the modules can be easily joinedtogether.

Starting point is a μ-LED with a horizontal architecture. The size ofthis optoelectronic component is designed to meet the requirements ofthe display sector, where the smallest chip sizes are required due tovery narrow pixel pitches, in terms of emission area (about 300 μm2 orless). In order to meet the requirements of other applications such asvideo wall, the μ-LED architecture is designed in such a way that by asimple adaptation of one process step, namely the use of another maskfor layer stack or mesa structuring, light emitting diodes can beproduced that consist of several subunits of this smallest μ-LED.

For example, the basic size for a base module is 15 μm×10 μm. With themask and a suitable contacting or separation, a component with 15 μm×20μm or 30 μm×30 μm would be just as easy to produce, which in turn issuitable for various μ-LED display applications. As already mentioned, acomponent comprises one or more base modules, which in turn may compriseone or more μ-LEDs.

The modular design with the smallest chip currently required as the baseunit or base module, with the possibility of converting it into a largercomponent with a multiple of the dimensions of the base unit, the basemodule, by only a minor adjustment during processing, saves resourcesduring development and opens up a certain freedom in the production ofsuch components. If, for example, applications in the μ-LED range with adifferent brightness or pixel pitch are required, the chips required forthis can be produced relatively easily.

In one aspect, not only the mesa (stack of layers) is structureddifferently, but also a contact layer. To do this, two steps are varied,but it is no longer necessary to ensure that all contact pads areconnected. By using a horizontal chip architecture, further processsteps for n-contact connection, such as for the vertical chip aftermounting on the target substrate, can be avoided. This can simplifymanufacturing and thus reduce costs compared to other manufacturingtechniques.

According to another aspect, the second contact can be formed by meansof a dielectric to the transition layer and the second layerelectrically insulated to and at the surface area of the second layerfacing away from the carrier.

Depending on the application requirements, base modules are designed asa matrix along an X-Y plane along at least one row and along at leastone column, with base modules of a respective row having the sameorientation. The base modules of two adjacent rows are oriented in thesame way if necessary. In this way, an electrical series connection ofbase modules can be easily implemented.

Alternatively, the base modules of two adjacent lines are oriented inopposite directions, whereby identical contacts are arranged adjacent toeach other. In this way, an electrical parallel connection of basemodules is easily realized. Since in horizontal μ-LEDs both contacts forn and p are located on the bottom side, it is advantageous to arrangethe chips alternately in rows. In a 2×X configuration of the chip, thecontacts for the p side for both base elements are located in the middleof the chip, the n contacts on the outside, thus minimizing the risk ofa potential short circuit.

Removal of the at least one light emitting diode module from theplurality of base modules is in some aspects carried out by means of adeep edge structuring through the first layer, in particular from theside of the second layer. It can be carried out by means of laserlift-off, namely from the side of a carrier facing away from the module.An etching process would also be conceivable.

Another aspect deals with the question whether and to what extent suchSub-units with sensor can be provided. For μ-displays especially in thefield of Augmented Reality but also for automotive applications, it canbe useful to provide sensors to record reactions or other parameters ofa user. For example, in an application in the field of AugmentedReality, one or more photo sensors can be provided in order to detectthe direction of gaze or a change from one direction of gaze. The amountof light can also be recorded, for example to brighten or darken animage. The same sensors can also be used for displays in automotiveapplications. Sensors can also be used to detect the driver's attentionin order to initiate measures if necessary in case of detected fatigue.

The inventors have recognized that future displays may not have sensorsthat are placed outside the display. Instead, the functionality ofsensors behind or in a full-surface μ-display should be made possible asan alternative to previous separate solutions.

The subdivision into μ-LED modules revealed here is used for thispurpose. Redundant places for subpixels can be equipped with sensorsinstead of μ-LEDs. According to a first aspect a μ-display with a targetmatrix is proposed, which is formed on a first carrier or end carrier.The matrix or μ-display has positions that can be filled with μ-LEDs. Inaddition, a number of components, in particular μ-LEDs, are formed on asecond carrier or replacement carrier, so that a start matrix with thesame spacing as the target matrix is created from positions that can befilled with components. Furthermore, the μ-LEDs are grouped on thereplacement carrier to form a number of modules and these modules areseparated from the second carrier, the modules being positioned andelectrically connected on the first carrier in the target matrix in sucha way that a number of positions which are unoccupied by componentsremain in the target matrix, at which at least one sensor element ispositioned and electrically connected at least in part in each case. Thevacant positions of the target matrix correspond in some aspects tosub-pixel positions or pixel positions.

Furthermore, the modules or sub-units of μ-LEDs disclosed in thisapplication are now provided. Their size or spacing corresponds to thecorresponding parameters of the occupiable positions of the targetmatrix. The subunits are grouped into modules and positioned andelectrically contacted on the target matrix in such a way that a numberof unoccupied positions remain in the matrix, to which at least onesensor element is at least partially positioned and electricallyconnected. Modules or sub-units are thus positioned on a display moduleor a display so that some positions remain unoccupied, which can thus beequipped with sensors. In this way, the sensors become part of thedisplay. This has several advantages. For example, light falling on thedisplay can be measured directly and then the illuminance of the moduleor even individual μ-LEDs can be adjusted depending on the location.

According to a second aspect, a process for the production of aμ-display is proposed. This has a target matrix with positions formed ona first carrier or end carrier and which can be occupied by μ-LEDs,arranged in rows and columns. The positions that can be occupied cancorrespond to subpixels. In addition, the locations show a size andspacing that substantially correspond to the modules disclosed herein.In other words, the target matrix comprises locations arranged in rowsand columns and can be occupied by modules of μ-LEDs.

The modules are now produced as shown here, for example with flat anddeep mesa etching and grouped into modules. The modules produced in thisway are removed from the replacement carrier and positioned in the freespaces on the target matrix on the end carrier and electricallyconnected to the end carrier. During this process, however, previouslydefined positions are left free. These are then filled with at least onesensor element each, which is positioned and electrically connected.

The end carrier can have line connections for the modules and theindividual μ-LEDs. In addition, in some aspects the end carrier alsoincludes at least one current source and/or control electronics for theapplied modules or μ-LEDs. In another aspect, the end carrier alsocontains the electronics for reading out the at least one sensorelement. The at least one sensor element can include a photosensor.Further examples are given below.

The prepared modules or sub-units of μ-LEDs and the corresponding areaof the target matrix on the final carrier must be identically gridded orhave the same size and, if necessary, the same periodicity. The spacingshould be the same, especially if larger modules with several rows orcolumns are transferred and applied to the final carrier.

In one aspect, one or more contact areas of a module or subunit arecongruent with a relevant contact area of occupiable positions on theend carrier. Thus, the modules can be integrated into the target matrixon the end carrier. The modules can thus be inserted or integrated intothe target matrix on the end carrier.

It is thus possible to construct a display in which the modules,especially the μ-LED modules, are arranged at the same distance fromeach other for all components. Thus, in one aspect, a target matrix of adisplay is assembled with a very small distance between the occupiablespaces. In this aspect, each place that can be occupied can be populatedwith the smallest module to be produced. This results in a display thatallows a very high resolution due to the small size of the pixels andthe small distance between them and due to which the display can bebrought very close to a user's eye.

Alternatively, it is possible to separate further the occupiablepositions of the target matrix. Likewise, in some aspects, several ofthe subunits revealed here can be arranged on such an occupiablelocation. In some aspects, the positions of the target matrix arrangedin rows or columns can each have a distance b from each other. The μ-LEDmodules each have the same size and a distance a from each other.Distance a can be equal to distanceb, which is substantially the same asabove. However, distance b can also be a multiple of distance a. Sincethe contact surfaces for the μ-LED module or subunit are also includedin the occupiable areas, the available space increases with a largerdistance b between the occupiable areas. In this way, larger modules canbe used or several modules can be combined. If, for example, thedistance b is 2.5 times the distance a, a module can be placed on anoccupiable position which is composed of 4 individual modules and thereis still a distance between the modules placed on adjacent positions.

This design allows different eye sensitivities and resolutions to betaken into account. The smaller the distancesa and b are, the higher theresolution, the less sensitive the eye of an user can be. Thus,different displays with different pixel or subpixel sizes and pixeldistances can be realized with the same μ-LED modules. This may be anadvantage in that μ-LED modules can be manufactured independently of thetarget matrix, its carrier and its wiring.

The already disclosed flat mesa etching, which serves for the electricalcontacting of the pixels and the formation of the μ-LED modules and thetarget matrix and in which etching is performed in the μ-LED grid, iscombined with a so-called deep etching, in which the chip grid and themodules can then be defined. This chip grid can differ from the pixelchip grid depending on the application. For example, one could thenproduce 2×2 large chips with 4 subpixels each (4 base units). One baseunit is one μ-LED each. By skilfully designing the mask for the secondmesa etching, one could also create pixels each comprising one base unitless. By stringing these pixels together, a display with “holes” in thesize of one base unit or multiples thereof is created. These “holes” or“missing subpixels” can then be used to accommodate various sensors, forexample. This combination makes it possible to create subpixels withredundancy, whereby in some cases the redundant subpixels are replacedby the sensor.

For this purpose, it is expedient that μ-LEDs are provided with auniform chip architecture and the same or easily variable size of chipsfor the production of displays. The techniques described here can beused for this purpose. When producing modules of the disclosed type, itis possible, for example, to use the cover electrode disclosed in thisapplication or the surrounding structure to increase the light yield. Insome aspects, the modules can be further processed afterwards, forexample by applying a photoelectric structure. At this point, however,it should also be mentioned that the μ-LED modules can already beprovided with such a structure in their manufacturing process. In someaspects, the μ-LEDs are combined into rectangular or square modules,which in turn can be combined in any way, especially into rows. Bymanufacturing by means of flat and deep etching, wafers can be preparedfrom such modules, which can then be separated as required for thetarget matrix. In this way, modules of different sizes can be realized.The free positioning makes it possible to leave specific positionsunoccupied. Groups of cells or even entire rows or columns can also beleft unoccupied. Finally, these modules can be used to equip displayswhose target matrix has a different arrangement of vacant positions,e.g. not in rows and columns.

According to an embodiment, at least one module can have four pixelelements in two rows and two columns. Each pixel element can compriseone or more subpixels. In another configuration, a module can have foursubpixel elements, which are also arranged in a 2×2 matrix. This is anembodiment easy to handle. In another embodiment, at least one modulecan have two rows and two columns, but only three components. This is anembodiment easy to handle, where an unoccupied position is alreadyprovided with the module.

In a further configuration, at least seven modules each with four pixelelements and at least two modules each with three pixel elements can bepositioned and electrically connected in the target matrix on the endcarrier in such a way that at least two positions unoccupied by pixelelements are created, at which in each case at least one sensor elementis positioned and electrically connected. Here, too, the modules can bedesigned as desired and can be linked to one another on the end carrieror positioned next to one another in such a way that vacant positionscan be generated in a targeted manner. Here too, the pixel elementseither comprise several subpixel elements and corresponding μ-LEDs oreach pixel element is itself a μ-LED.

According to a further embodiment, the positions occupied by sensorelements can be framed by components. In this way, clearly definedpositions, positions not occupied by components, can be explicitlyprovided for sensor elements.

In some aspects, the modules can be created as subpixels. Modulesemitting in different colors may have been created on different secondor substitute carriers.

According to various embodiments, a large number of sensor elements maybe configured as part of a sensor device formed on the first carrier orend carrier to receive electromagnetic radiation incident on a firstside of the first carrier. In this way, different radiation spectra canbe detected depending on the application. According to a furtherembodiment, a sensor element can be formed as a photodiode, in the formof a phototransistor, in the form of a photo-resistor, in the form of anambient light sensor, in the form of an infrared sensor, in the form ofan ultraviolet sensor, in the form of a proximity sensor or in the formof an infrared component. The sensor can also be a vitality sensor thatrecords a vital parameter. The display device is therefore versatile. Avital sign can, for example, be the body temperature.

In another configuration, the vital sign monitoring sensor may belocated within a display screen or behind the rear surface of a displayscreen, the sensor being designed to measure one or more parameters of auser. In addition to body temperature, this parameter includes, forexample, the direction of vision of the eye, pupil size, skin resistanceor similar.

According to a further design, a component can have a first layer formedon a carrier, on which an active transition layer is formed and on whicha second layer is formed. A first contact is connected to a surface areaof the second layer facing away from the carrier, and a second contactis connected to a surface area of the first layer facing away from thecarrier. This embodiment corresponds to a vertical μ-LED. In this way,the components can be contacted from only one side. In further aspects,the second contact can be electrically insulated from the transitionlayer and the second layer by means of a dielectric to and on thesurface area of the second layer facing away from the carrier.

In addition to the production of monolithic pixel arrays, μ-LEDs canalso be applied to a carrier board and subsequently contacted. Due tothe size of individual μ-LEDs, they are difficult to transfer andcontact individually. For this reason, for some applications in theautomotive sector, video walls or in special cases in augmented realityapplications, μ-LEDs are first applied to a slightly larger carrier andthen contacted with leads on a circuit board. The circuit board canagain be a video wall, pixel matrix or a similar screen arrangement.Such arrangements sometimes require special connection techniques, whichalso differ from arrangement to arrangement and technology ormanufacturing process. This makes the provision of different μ-LEDs ormodules with such devices quite complex.

Thus, there is a need to Pixel module for different mounts which meetvarious requirements and are particularly suitable for manufacturingprocesses for video wall NPP of different generations, i.e. also for LEDmatrices in AR or VR applications or flexible displays in the automotivesector.

In one embodiment, a μ-LED module comprises a body with a first mainsurface and four side surfaces. At least three contact pads are arrangedon the first main surface. These are designed to be connectedelectrically to one optoelectronic component each. For example, thethree, or a subset of these are connected to a μ-LED with an edge lengthof 10 μm or less. According to the proposal, several contact bars arealso provided. Each contact bar electrically connects one of the atleast three contact pads. In addition, the contact webs on the firstmain surface lead to at least one of the four side surfaces. In otherwords, the contact bars are arranged on the first main surface and theat least one of the side surfaces. The contact bars form contact lugs onthe side surface, i.e. they are designed for external contacting.

With the proposed μ-LED module, rewiring is thus possible, so that themodule can be easily connected to the predefined connection points on acarrier or matrix. In particular, the significantly smaller μ-LEDs onthe module can be arranged in advance, so that additional space forelectrical connection is created with the module. This allows a higherflexibility and the use of such modules for different applications.

In addition to a module with three μ-LEDs, which can be combined intoone pixel, for example, several μ-LEDs can also be combined into alarger module in this way. The individual μ-LEDs can be manufacturedseparately, allowing the optimum technology for the respective μ-LED tobe used. Single μ-LEDs can also be designed redundantly. Larger modulesare also called segments. Beside single μ-LEDs, special modules withflat and deep mesa etching, as shown here, can be used. A design in barform or with the proposed antenna structure would also be conceivable.The proposed rewiring allows modules and μ-LEDs to be manufacturedindividually and adapted to the respective application.

In one embodiment, the contact ridges only run along the sidewalls, inanother embodiment they are also connected to contact pads on a secondmain surface, the underside of the μ-LED module. This means that thereare contact pads on both the upper side (for the μ-LEDs) and the lowerside of the μ-LED module. This makes the μ-LED module suitable for bothSMT (surface mounted technology) manufacturing processes as well as forcontact bar processes in which contact bars on the carrier are broughtup to the side surfaces of the module. The design makes the module moreflexible and can also better compensate for manufacturing tolerances ofthe carrier (e.g. in contact bar length or size).

In a further embodiment, a second side face of the four side faces willonly have the fourth contact web. This contact bar can be marked, forexample, to be loaded in operation with a special potential. Inaddition, it can also differ optically from the other contact bridges,for example by its size on the side surface. This ensures that themodule is placed in the correct position during transfer. In anotherembodiment, two of the three contact bars are arranged on different sidesurfaces. In one example, four contact ridges are provided, each ofwhich is arranged on one side surface and preferably connected to acontact pad on the underside of the module, i.e. the second mainsurface.

In another example, contact bars are also arranged on the first mainsurface. These run to the edges and then along the edges of the sidefaces in the direction of a second main face, e.g. the bottom of themodule.

Another aspect concerns the configuration of the module body. Forexample, the body of the module comprises a prism with the base of arectangle or other square surface. In one embodiment, a second mainsurface is provided, which is opposite the first main surface andcomprises a larger area than the latter. Alternatively, the first mainsurface may be designed to form an angle of 90° or more with each of thefour lateral surfaces. This forms a prismatic or square truncatedpyramid. In another configuration, the side faces are not perpendicularto the first major surface.

In a further aspect, the contact bars and/or contact pads comprise a, inparticular vapour-deposited, metal tag, the thickness of which is lessthan 5 μm, in particular less than 2 μm or even less than 1 μm. Forexample, a thickness of the contact bars and contact pads can be in therange of 100 nm to 50 nm. These can be produced by appropriatephotolithographic processes. Depending on the design, the metal tags andcontact pads can also be deposited on an insulating layer of the modulebody, for example by MOCVD or similar processes. Contact pads on thebottom side can be produced in a separate step. In a further embodiment,the module body comprises at least one through-hole plated at leastpartially filled with an electrically conductive material, theelectrically conductive material on the first main surface beingconnected to or forming one of at least three contact pads arranged onthe first main surface.

The module body can be configured with continuous main surfaces. Inanother configuration, the body may comprise a recess on the first orsecond main surface in which at least a contact bar runs. A contact baron the second main surface can be connected to a via and lead to acontact pad. Likewise, a contact bar can connect at least one μ-LEDarranged on the first main surface to the through-hole plating.

The body can contain or be formed from silicon. It can be surrounded byan insulating layer, for example silicon dioxide, to prevent a shortcircuit. The silicon material may be free at one point to which areference potential can be connected. Vias through the body are alsolined with insulating material. Contact bars and contact pads areapplied to the insulating layer. The module body can have a thickness ofless than 30 μm, especially in the range of 5 μm to 15 μm. This allows avery low overall height of only a few 10 μm to be achieved. The overallheight of the module can be further reduced by an additional recess inwhich the optical components are inserted.

Another aspect relates to a process for manufacturing a μ-LED module inwhich, among other things, a membrane wafer is structured so that it hasa large number of substantially V-shaped trench-shaped recesses. Thedepressions are designed in such a way that a first main surface of thestructured membrane wafer bounded by trenches forms an angle of 90° orgreater with the flanks of the trenches. Then, several contact pads aregenerated on the first main surface of the membrane wafer. Optionallyand/or additionally, leads, contact tabs and contact bars can begenerated on the first main surface and the side surfaces. Then at leastone optoelectronic component, in particular a μ-LED, is applied to themodule and electrically conductively connected to a contact pad. In asubsequent step, a temporary carrier is provided and the membrane waferis etched back up to or just before the trenches after rebonding withthe temporary carrier. Finally, backside contacts are applied andoptionally separated.

As already explained, in monolithic arrays a pixel error can be reducedby providing a redundant subpixel. Electrical crosstalk is avoided,while optical crosstalk between the redundant subpixels is stillpossible. A similar problem exists with separated pixels. Although itmay be possible to test the functionality before separating, due to thesmall size of μ-LEDs during transfer to the backplane in production,positioning or connection errors may occur. In addition to continuousimprovements of the process steps in manufacturing, there is theapproach to make each pixel of a Pixel array with redundant μ-LEDs ormore precisely, to provide redundant positions on which μ-LEDs can beplaced. This can mean, for example, that for each RGB subpixel of apixel two or more μ-LED chips are used instead of just one μ-LED chipfor one color, which leads to an overcrowding of subpixels per pixel formost pixels. Another approach is to repair defective subpixels of apixel. After a function text, faulty subpixels are switched off andreplaced by working subpixels.

A method of making an array of pixels or an array of pixels comprisinginter alia providing a substrate for arraying pixels on the substrateand electrically contacting the pixels, the substrate providing a set ofprimary contacts for a pixel, the set of primary contacts of the pixelbeing for electrically contacting a group of sub-pixels of the pixel,the substrate providing a set of spare contacts for the pixel.

Then the primary contacts of the pixel are equipped with a group ofμ-LEDs, whereby the set of spare contacts of the pixel is not equipped.Then defective μ-LEDs in the group of μ-LEDs are identified and one ofthe possibly several replacement contacts of the set of replacementcontacts of the pixel is equipped with a replacement subpixel for thedefective μ-LED. In this context, a pixel may comprise one or moresubpixels. The pixel may also be configured for the connection of avertical or a horizontal μ-LED. Accordingly, a primary contact cancomprise at least one contact area (in the case of a vertical μ-LED) ortwo contact areas (when equipped with horizontal μ-LEDs). One of the twocontact areas can be used by several μ-LEDs, including the redundantone. If equipped with vertical μ-LEDs, one of the cover electrodespresented here may be provided. The pixel field can also be surroundedby a surrounding mirror layer.

In addition to separate μ-LEDs, the μ-LED modules or base modulesdisclosed here can also be assembled. For example, a μ-LED module cancomprise two base modules, so that one base module is provided as aredundant unit.

The method according to the invention thus allows the assembly of theprimary contacts for each pixel of a pixel field with a designated groupof subpixels. One primary contact is equipped with one subpixel each. Ineach pixel, the defective subpixels on the primary contacts can then bedetermined. For an identified, faulty subpixel in a pixel, a replacementcontact for the pixel is fitted with a replacement subpixel in asubsequent step. Thus, only one replacement contact in a pixel isequipped with a subpixel to replace functionally a subpixel identifiedas faulty on the primary contacts.

A redundant assembly of the pixels with several subpixels of the samecolor is therefore not necessary. In comparison to the redundancyconcepts known from the state of the art, much fewer subpixels are usedin a pixel field to be produced, since an increased assembly is onlycarried out after the identification of faulty subpixels. Themanufacturing costs can thus be reduced.

In addition, control techniques can be used in this application to testthe functionality of a μ-LED on the one hand and to disconnect safelythe faulty μ-LED in case of a failure, especially in case of a “SHORT”by melting a fuse or other measures.

This allows the faulty one to remain on the pixel, thus eliminating theneed for additional process steps.

It is also possible to refill the replacement contacts for a pixelindividually if faulty subpixels are identified. It is also possible toreplenish the spare contacts of a pixel several times, following furtherfunctional tests in a continuous processing. This increases theprobability of success of the placement process. In addition, it ispossible to reproduce subpixels, e.g. in the form of μ-LED chips, withselected characteristic data, for example to achieve a correct colorcalibration in a particular pixel.

according to an embodiment, the steps of identifying a defectivesubpixel in the group of subpixels and providing a replacement contactwith a replacement subpixel for the identified subpixel may be repeateduntil there replacement subpixel it attached to the pixel for eachsubpixel identified as defective. For all defective subpixels of apixel, the substrate can thus be populated with replacement subpixels ina subsequent process step.

According to another aspect, a subpixel identified as faulty does notneed to be removed if the faulty pixel is declared “OPEN”, i.e. noleakage current flows through the damaged or destroyed pixel. Circuitrymeasures can also be provided to separate an electrical contact for anidentified, faulty subpixel. A current flow to the faulty subpixel whenoperating the pixel array can thus be avoided. Corresponding conceptsare disclosed in this application and can be used for this purpose.

Compared to repair concepts, the process of removing defective subpixelscan be omitted. This makes the manufacturing process faster and morecost-effective. The risk of damaging the pixel field when removingdefective subpixels is eliminated. A repair by removing a defectivesubpixel allows the further use of the primary contact area that becomesfree. However, residues and damage reduce the probability of success ofa second placement and bonding process. The replacement contactsprovided are free of residues and damage.

It may be provided that a subpixel identified as defective and thereplacement subpixel are intended to emit light of the same color. Afaulty subpixel is thus replaced by a replacement subpixel, which atleast approximately emits the same color, as the faulty subpixel wouldhave if it were functional.

The group of subpixels of a given pixel can comprise one or more sets ofRGB subpixels. RGB stands for red, green and blue. The group ofsubpixels can therefore have three subpixels, for example. One subpixelcan be configured to emit red light, another subpixel can be configuredto emit green light, and yet another subpixel can be configured to emitblue light. By additive mixing of the three basic colors red, green andblue, any or nearly any color can be generated in a known manner.

The group of subpixels can also have more than one subpixel to createeach primary color. For example, the group of subpixels can have 6subpixels, with two subpixels each for creating red, green, and blue,respectively.

According to an embodiment, it is intended that no replacement contactof the pixel is equipped with a replacement subpixel if no defectivesubpixel is found in the pixel. The pixel field can therefore containpixels for which the replacement contact or contacts are not fitted.

Another aspect deals with the design of the primary contacts. These areconfigured for anode-side and/or cathode-side contacting of thesubpixels of a pixel. For example, the contacts can be configured insuch a way that so-called flip chips can be arranged on these contactsand electrically connected. Flip chips are optoelectronic chips whoseelectrical p and n contacts are on the same surface side. Thereplacement contacts can also be configured for contacting thereplacement sub-pixels of a pixel on the anode side and/or the cathodeside. The redundancy of the contact areas for the subpixels of arespective pixel achieved by the replacement contacts can thus relate toboth the cathode and the anode of a subpixel or only to one of the twoconnections.

In this context, a subpixel or replacement subpixel is formed by aμ-LED, which is placed on the respective contact and connectedelectrically and mechanically. Equipping the replacement contact with areplacement subpixel for the subpixel identified as defective can bedone independently of the color of the light emitted by the replacementsubpixel. Normally, each primary contact is populated and only thereplacement contacts of the μ-LEDs declared as faulty. However, aprimary contact does not have to differ from a secondary contact interms of circuitry or even its structure on the surface. In thisrespect, a combined assembly can therefore also be carried out. In thiscontext, it can also be said that the first contact assembled by a μ-LEDof a color represents the primary contact.

The proposed concept also concerns a pixel array with a substrate for anarray of pixels arranged on the substrate and for the electricalcontacting of the pixels, where the substrate provides a set of primarycontacts for a pixel. The set of primary contacts is intended forelectrical contacting of a group of sub-pixels. The substrate alsoprovides a set of spare contacts for the pixel. According to theproposed principle, the primary contacts are populated with the group ofsubpixels, wherein the group of subpixels comprises a faulty,deactivated subpixel, and wherein a replacement contact of the set ofreplacement contacts of the pixel is populated with a replacementsubpixel as a replacement for the faulty, deactivated subpixel.

With at least two pixels of the pixel field, the number of occupiedspare contacts may be different. This results from the fact that in apixel the spare contacts are only populated with spare subpixels ifsubpixels on the primary contacts are identified incorrectly.

The above concepts for reducing defect or crosstalk improve the yield offunctional elements during production. Several aspects deal withmeasures to improve a transfer of μ-LEDs. For this purpose, μ-LEDs arenow increasingly being developed, whose edge lengths are usually lessthan 100 μm, often between 70 μm and 20 μm. For special applications inthe field of augmented reality, the dimensions are also less than 20 μm,for example in the range of fpm to 10 μm or even fpm to 5 μm.

One of the technical challenges associated with μ-LEDs is in particularthe manufacturing process, since a large number of μ-LEDs not only haveto be produced but also installed in matrices or modules. In order toproduce such modules or even larger displays, the μ-LEDs produced aretransferred either as individual chips or ready in the modules presentedhere to a carrier surface of the module or display, where they are fixedand electrically connected. With several million LEDs to be transferred,this process is critical in terms of speed and accuracy.

Various processes are known for this, such as the transfer printingprocess. These use a flat stamp to simultaneously pick up a large numberof μ-LEDs from a wafer, move them to the carrier surface of thesubsequent display and precisely assemble them there to form alarge-area overall arrangement. An elastomer stamp, for example, can beused for this purpose, to which the individual μ-LEDs can adhere withoutbeing mechanically or electrically damaged thanks to suitable surfacestructures and material properties. Depending on the process technology,this can be problematic, as the μ-LEDs can tilt, shift or twist whenthey are detached. It is therefore desirable to enable the mounting ofμ-LEDs with reduced holding forces or damage.

The aspects and ideas described in the following are based on thefollowing considerations: When using mass transfer processes, i.e. thesimultaneous localized relocation of a large number of semiconductorchips, the μ-LEDs are picked up or lifted from a wafer with the aid of asuitable tool. This requires the chips to have an exact and determinableposition on the wafer, for example to be able to position a tool such asan elastomer stamp with its cushion structures as precisely as possibleover the respective μ-LED. At the same time, a surface structure shouldalways be homogeneously and uniformly positioned in space so that atransfer tool can attach itself to a chip surface in a standardizedmanner with a high probability of success.

According to a first aspect, a method for providing a μ-LED is proposedin which a first electrically conductive contact layer is arranged on afirst main surface side of the functional layer stack facing away fromthe substrate. The layer stack is configured as an optically activelayer stack and accordingly forms in particular a μ-LED. Then at leastone support layer attached to the substrate is provided which carriesthe μ-LED. Due to the holding structure, the contacted functional layerstack can be broken off during lift-off. Subsequently, a sacrificiallayer, which is applied between a second main surface side of thefunctional layer stack facing the substrate and the substrate and inparticular comprises AlGaAs or InGaAlP, is at least partially removed.After the partial removal, a second electrically conductive contactlayer can be applied to the second main surface side of the functionallayer stack in the area of the removed sacrificial layer

In the process presented here, lithographic processing of a functionallayer stack takes place only on one side of a substrate, thus avoidingadditional rebonding if necessary. The holding structure can in turn belithographically adapted to the requirements, the size of the layerstack and other parameters. At the same time, the layer stack iscontacted on both sides, thus forming a vertical μ-LED.

According to a second aspect a μ-LED is proposed, which comprises afunctional layer stack. A first electrically conductive contact layer isattached to a first main surface side of the functional layer stackfacing away from a substrate and a second electrically conductivecontact layer is attached to a second main surface side of thefunctional layer stack facing the substrate. In this case, the contactedfunctional layer stack is supported, in particular freely, by at leastone holding structure attached to the substrate. The holding structureallows the contacted functional layer stack to be broken off in furtherprocess steps during lift-off. Accordingly, the layer stack or the μ-LEDexhibits a break-off edge after lift-off and in all subsequent processsteps.

With the measures proposed here, no rebonding is necessary and a simplealignment of a lithographic masking is possible. The formation of avertical μ-LED is possible just like a horizontal LED. Absorption isreduced and light extraction through the horizontal surface isincreased, whereas thinner epitaxially generated layers are possible.Without bonding, the epi-structure of a layer sequence is subject toless mechanical stress. In addition, the sacrificial layer allows a moreprecise etching process, since the etching process can be very selectivefor the sacrificial layer. The contact layer can therefore be madethinner.

In some aspects, the support structure may in particular include InGaAlPor AlGaAs or BCB or an oxide, for example SiO2, or a nitride or acombination of such materials, and in particular be electricallynon-conductive. In this case, it can also be configured to passivate thestack of layers. The support structure can be at least partiallyepitaxially grown or generated by vapour deposition or electroplating.In contrast, the sacrificial layer can have AlGaAs or InGaAlP and can beetched away wet-chemically. The first and/or second electricallyconductive contact layers can be produced by sputtering, vaporizing,galvanically or epitaxially. The contact layers can be transparent andcontain ITO or ZnO or a metal. In order to avoid oxidation ordegradation, some aspects are provided for, one flank of the contactedfunctional layer stack must be covered by a passivation layer.Alternatively, it would be possible to diffuse a metal, in particularZn, from one flank of the contacted functional layer stack into an outeredge region of the functional layer stack. This changes the bandstructure in the edge area and thus keeps charge carriers away from thearea affected by an increased defect density.

In order to securely attach the retaining structure, it can extend intothe substrate from the first main surface side of the functional layerstack.

According to a further embodiment, a first supporting layer, inparticular comprising InGaAlP and/or AlGaAs, can be formed on thefunctional layer stack on the first main surface side thereof, to whichthe first electrically conductive contact layer can be attached, thefirst supporting layer and the first electrically conductive contactlayer being attached to the substrate at least at one point and thustogether can provide the holding structure.

Another point of view deals with the question how a Avoidance ofbreakage edges and improved lift-off can be achieved.

A solution is proposed here, in which a mechanical connection betweenthe μ-LED and a surrounding or underlying substrate is maintained usingcrystalline, dielectric support structures. However, this mechanicalconnection is configured in such a way that on the one hand it reliablyholds the μ-LED chip in place mechanically, but on the other hand itbreaks when the smallest possible bending force or tensile force isexerted, thus releasing the chip for removal.

In particular, a carrier structure is proposed to accommodate flatmicrochips or μ-LEDs. A carrier structure in this context means anarrangement that can accommodate a plurality of such μ-LEDs, for examplewith edge lengths in the range of 5 μm to 20 μm or smaller. The mainpurpose here is to achieve a mechanically stable fixation, for examplerelative to a grid or a matrix, making the best possible use of theavailable space. Furthermore, this carrier structure should be suitablefor providing the large number of microchips for transfer with the aidof a transfer tool.

The carrier structure also has at least two receiving elements that areconnected to the carrier substrate. A mounting element in this case isto be understood as a mechanism or functional element that is suitablefor fixing a μ-LED spatially by mechanical contact, if necessary ininteraction with other mounting elements, or for holding it in a definedspatial position. A mounting element can have diameters in the range of1 μm, for example. In one example, a microchip is attached to twopicking up elements.

In some aspects, the carrier structure comprises a flat carriersubstrate. Such a carrier substrate can be, for example, a wafer, afoil, a frame or similar from the field of semiconductor production. Inaddition to its function as a base plate or base material for thesemiconductor manufacturing process, a wafer can also provide a supportor carrier function in preparation for a subsequent mass transfer. Inaddition, flexible materials such as films are also suitable as carriersubstrates.

According to an example, a receiving element can be configured in acolumnar, pillar-like or pile-like manner starting from the carriersubstrate. In one embodiment, the microchip rests at its corners oredges on the at least two receptacle elements partially but notcompletely. The mounting elements are connected to the carrier substrateand are designed to hold a microchip detachably between the at least twomounting elements in such a way that μ-LED can be moved out with adefined minimum force perpendicular to the plane of the carrierstructure.

In other words, on the one hand, a sufficiently secure hold of the μ-LEDby the mounting elements should be achieved, on the other hand, thepossibility should be deliberately created to detach the μ-LED with aslittle force as possible and, for example, to feed it to a transfertool. For this purpose, it may be necessary to provide a contact surfacefor each support element that is smaller than 1/20, in particularsmaller than 1/40 and in particular in the range from 1/80 to 1/50smaller than the chip area of the μ-LED. In an alternativeconfiguration, an edge length of the μ-LED is at least by a factor of10, in particular at least by a factor of 20, greater than an edgelength of the support element.

“Detachable” is to be understood to mean that there is no permanent,e.g. materially coherent connection such as fusing, gluing or similarbetween the microchip and the receiving ele-ment, but a non-destructive,detachable connection. The attachment can be based on a physicalconnection, such as an adhesive connection by Van-De-Waal forces orelectron bridges. The same can be given by different materials and asuitable selection of them between the μ-LED and the receiving elements.This is intended in particular to avoid breaking or similar processesthat would involve the destruction of material structures with thecorresponding fragments, particles or splinters. Instead, alternativeadhesion mechanisms such as the exploitation of mechanical friction ordelamination are used here. In particular, known limited or restrictedadhesion properties of materials or material combinations are exploited.According to an example, the μ-LED is placed between two or more holdingelements.

At the contact surfaces, for example, adhesive forces or other adhesionforces arise, which allow mechanical fixing of the μ-LED in space. If adefined minimum force is applied to the μ-LED, e.g. by an attachedtransfer tool, this results in detachment forces at the contact surfacesbetween the μ-LED and the mounting elements. This defined minimum forcecan be influenced by a suitable selection of materials or materialcombinations at these contact surfaces.

The contact surfaces or overlaps can, for example, comprises an areadimension in the range of 0.05 μm² to 1 μm². In this case it isdesirable to achieve a secure hold of the μ-LED on the carrier structureon the one hand. On the other hand, it is substantial for an effectiveand fast mass transfer of the μ-LED that the μ-LEDs can be liftedupwards and detached with as little force as possible. For this purpose,it may be necessary to provide for a ratio between the contact area ofeach element and chip and the total chip area of less than 1/20, inparticular less than 1/40 and in particular in the range from 1/80 to1/50 smaller than the chip area. In an alternative configuration, anedge length of the μ-LED is at least by a factor of 10, in particular atleast by a factor of 20, greater than an edge length of the receivingelement. The available area of the pick-up element may be larger, butthe μ-LED rests on only a part of this area. The contact area of thechip is therefore at least 20 times, in particular at least 40 timessmaller than the total chip area.

A suitable compromise must be found here, for example by the appropriateselection of materials or material combinations and the dimensioning andplacement of the contact surfaces. The defined minimum force can also beinfluenced by designing the size and shape of these contact surfaces.Large contact areas consequently lead to a higher minimum force requiredto detach the μ-LED from the carrier structure. In addition to holdingprinciples caused by friction or lamination, magnetic, electrical orsimilar holding forces are also conceivable.

According to another example, it is also possible that the carrierstructure has only one single holding element to hold a μ-LED. Due tothe low weight of the semiconductor structures, it is conceivable that acontact surface between the single holding element and the μ-LED, whichis suitable in its shape and sufficiently dimensioned in terms of itssize, could provide sufficient hold in combination with a suitably highminimum force for detaching the μ-LED.

In one embodiment, a substrate for the production of the μ-LEDs can alsoserve as a carrier structure. In such a case, a sacificial layer may beprovided. During the manufacturing process, the μ-LED is connected tothe growth substrate. To expose the finished μ-LED, for example, thisintermediate sacrificial layer is removed by gas or plasma-based etchingprocesses so that a gap is created between the μ-LED and the wafer. Athickness of the sacrificial layer is, for example, 100 nm (nanometers)to 500 nm. The idea here is that when the sacrificial layer is removed,the receptacle elements take over a holding function for the μ-LED onthe carrier structure. The mounting elements can have the shape of ananchor.

A pull-off of the μ-LED is usually done in a direction away from thecarrier substrate, with a force vector that is at least partiallyperpendicular to a carrier substrate plane, which is to be understood inx-y-direction. The pick-up elements remain on the carrier substrate andin particular do not break. Thus, no residues of the pick-up elementremain on the μ-LED, which could cause problems during subsequentprocessing. According to an aspect, at least one mounting element isconfigured to simultaneously hold and/or support another, adjacentlyarranged μ-LED. The considerations regarding this feature can besummarized as follows: Holding structures for μ-LEDs often requirespace, which ideally should be minimized in order to achieve a higheryield on a wafer. Due to the manufacturing process, the μ-LEDs in turnare arranged next to each other on a wafer in a regular structure.

There are gaps in between due to the process. The inventors now proposeto position a mounting element between two adjacent μ-LEDs so that thisone mounting element supports or accommodates several adjacent μ-LEDs.The advantage here is that less than one entire holding structure percomponent can be achieved mathematically. This can reduce the totalnumber of holding elements, thus saving space and consequently costs. Inaddition, an overall chip yield remains substantially constant, since noadditional space is required for the holding structure on the wafer,which would be at the expense of the number of μ-LEDs.

For example, a receptacle element may have contact surfaces arrangedopposite one another, which are then in mechanical contact with theadjacent μ-LED in this direction. The pick-up elements can then bedistributed and arranged over a surface of the carrier substrate in sucha way that a minimum number of pick-up elements are used to hold theμ-LEDs securely. This can be advantageous, for example, for theeffective use of a transfer tool to enable effective and fast pick-up ofthe μ-LEDs. According to an aspect, the mounting elements are arrangedon the carrier substrate in such a way that one μ-LED is held by exactlythree mounting elements. The choice of three holding elements can be anadvantageous compromise in that a good spatial stabilization incombination with a favorable distribution of the holding forces can beachieved. A shifting or tilting, especially in lateral direction on thecarrier substrate can be effectively prevented here. In doing so, asupport element can act on the microchip at different lateral areas inthe X-direction and Y-direction, for example in the center, off-centeror at an edge or corner. Several pick-up elements can also be arrangedon one and the same side of a μ-LED.

According to an aspect, a delamination layer is provided on the μ-LED oron the mounting element to move the μ-LEDs out of the carrier structure.The term “delamination” is used here to describe a detachment processthat occurs when two surfaces, or more generally, the connection of twolayers, come into contact. This can affect similar materials, but alsomaterial connections or different material surfaces.

The deliberate creation of a so-called delamination layer is intended toprevent breakage or material-destroying or structure-altering processesand instead cause non-destructive separation of the layers or surfacesfrom one another. Certain combinations of materials can be used, forexample a combination of SiO₂ and Al₂O₂, but also the use ofnon-oxidizing metals such as silver, gold or similar materials incombination with a dielectric such as SiO₂ In one aspect, the surface ofthe picking up element is thus surrounded by the delamination layer, sothat the delamination layer is formed between the μ-LED and the pickingup element. The delamination layer can only be a few nm thick, forexample in the range of 5 nm to 50 nm. The delamination layer can alsobe formed as an etch stop layer in one aspect or optionally extend overother parts of the carrier structure.

According to an aspect, the picking up elements are arranged in 5a mesatrench of a semiconductor wafer. As already mentioned, an optimal use ofspace on a wafer to increase the yield is generally desirable. Holdingstructures for μ-LEDs often require additional space. In themanufacturing process, various process steps are used to createthree-dimensional structures in which, for example, a μ-LED is formed atthe end as an elevation or mesa. So-called mesa trenches are formedbetween these individual μ-LEDs.

The term mesa trench is used to describe a comparatively steep flanklike feature on the sides of a μ-LED, whereby the trench, i.e. the areawithout epitaxy, references the deep structure in between. For example,the mesa can have a slope steepness in the range of 30° to 75°,especially of 45°. The idea here is to place the pick-up element exactlyin this already available spatial area without taking up additionalspace on the wafer. This allows a better utilization of the availablespace on the wafer.

According to an aspect, the supporting structure and the receivingelements are made in one piece. This can mean, for example, that thereceiving elements are part of the carrier substrate. The carriersubstrate can be a wafer, but also a PCB board, foil, frame or similarstructure. In the latter cases, this means that the mounting elementsthemselves are made of a different material and/or structure than thecarrier substrate. This can be achieved in a manufacturing process, forexample, by preserving the originally existing wafer structures in alocally limited manner through the various process steps and notremoving them by etching processes, for example. These structures thenserve as holding elements and holding structure for the finished μ-LEDs.

In one aspect, the mounting elements are designed to hold a μ-LED on theside and from a lower side of the μ-LED. In order to hold a μ-LED on anunderlying carrier substrate, it can be useful on the one hand to createa partial contact surface or bearing surface that provides a mechanicalstop in the Z-direction, i.e. in the direction of the carrier substrate.At the same time, a spatial fixation in lateral direction, i.e. inX-direction and Y-direction, can be achieved by additionally providing alateral stop. In this way, a stable spatial fixation can be achieved inthe direction of the carrier substrate and in the lateral direction onthe one hand, and on the other hand, a slight lifting of the μ-LEDs awayfrom the carrier substrate in the Z-direction can be made possible by atransfer process or a transfer tool.

In one aspect, the mounting elements have μ-LED holding surfaces thatslope away at an angle relative to the carrier substrate plane, so thatwhen the μ-LEDs are moved away from the mounting elements, a holdingforce on the μ-LED is reduced. In other words, the holding surfaces moveaway from the μ-LED the further the μ-LED is moved in the direction awayfrom the carrier substrate. This can also be understood to mean that aholding force is successively reduced when the μ-LED is lifted away fromthe carrier structure by a transfer tool, for example. This is primarilyintended to reduce the force required to pull off the μ-LED, inparticular to reduce runtimes of the process steps and to increase thequality of a transfer process.

Traditionally, there are various ways of transferring chips from acarrier wafer to a corresponding target substrate.

State of the art transfer processes such as laser transfer printing or“self-assembly” of individual micro light emitting diode chips from asolution or electrostatically activated or diamagnetic transferprocesses are known.

An extension of these concepts is achieved with the electro-statictransfer explained in more detail. A method is to be specified withwhich optoelectronic semiconductor chips with particularly smalldimensions, i.e. μ-LEDs, can be picked up and deposited and at the sametime, those μ-LEDs, which have certain defects, can be sorted out.Furthermore, a corresponding device for picking up and depositingoptoelectronic semiconductor chips is to be created.

The proposed concept is based on the aspect that electron-hole pairs aregenerated in μ-LEDs and generally in optoelectronic semiconductor chips.The μ-LEDs may each have a semiconductor layer with a photosensitiveregion, also called optically active region. In the optically activeregion, charge carriers or electron-hole pairs can be generated byappropriate excitation, especially by incident light. An electron-holepair consists of a defect electron and an electron, which has beenbrought from its ground state in the crystal to an excited state by theabsorption of energy.

The electron-hole pairs can be separated from each other by suitableproperties of the semiconductor material, such as two regions withdifferent concentrations of dopants, like a p-n junction. As a result,charges are generated in the respective semiconductor chips, whichcreate a dipole field outside the semiconductor chips. This process isalso known as the photovoltaic effect. The strength of the dipole fieldgenerated by a particular semiconductor chip depends on the propertiesof the semiconductor chip. Semiconductor chips can have defects, such asshort circuits, shunts or reduced efficiency, which typically lead to anaccelerated discharge of the charges generated by the excitation andthus to a reduced dipole field. Furthermore, according to the proposedmethod, a pick-up tool is provided, which serves to pick up the μ-LEDsor the optoelectronic semiconductor chips and to place them atpredetermined positions or locations, for example on a board on whichthe μ-LEDs are to be mounted. This process is also referred to as “pickand place” in the English language technical literature. It is alsointended that the pick-up tool generates an electric field at least atcertain locations, for example by being electrically charged at theselocations. The μ-LEDs are picked up by the pick-up tool during or afterthe generation of the electron-hole pairs.

The electric field generated by the pick-up tool interacts with thedipole fields of the optoelectronic semiconductor chips, creating anattractive or repulsive force between the pick-up tool and theoptoelectronic semiconductor chips. The electrostatic interaction orforce can superimpose an interaction or force that exists between thepick-up tool and the optoelectronic semiconductor chips even without theelectric dipole fields caused by the electron-hole pairs. For example, avan der Waals attraction or an electrostatic attraction can existbetween the pick-up tool and the respective optoelectronic semiconductorchips even without the dipole charge generated by the excitation. Theadditional electrostatic attraction makes it possible to overcome athreshold above which the μ-LEDs are released from a carrier on whichthe μ-LEDs are arranged and are picked up by the pick-up tool.

The force required to remove the optoelectronic semiconductor chips fromthe carrier may be greater than the force required to hold the removedoptoelectronic semiconductor chips by the pick-up tool. Therefore, theelectrostatic force may only be required to remove the optoelectronicsemiconductor chips and not to hold them. Consequently, the presence ofthe electric dipole fields is only necessary to remove theoptoelectronic semiconductor chips, but not necessarily to hold theoptoelectronic semiconductor chips afterwards.

μ-LEDs with certain defects, for example short circuits, shunts, lowefficiency or other defects, have a lower dipole field when excited thanμ-LEDs without such defects. Accordingly, the electrostatic interactionbetween the pick-up tool and the defective μ-LEDs is so small that thelatter cannot be picked up by the pick-up tool and remain on thecarrier. In other words, the electrostatic interaction between thepick-up tool and the μ-LEDs is selected in such a way that only infunctioning μ-LEDs is the acting force sufficiently strong. In otherwords, the electric field generated by the pick-up tool is chosen sothat only in interaction with functional μ-LEDs is the resultingelectrostatic force sufficient to lift the μ-LEDs off. For defectiveμ-LEDs that have a lower dipole field, the interaction is notsufficiently strong.

Therefore, the concept presented here makes it possible that defectiveμ-LEDs are not picked up and, accordingly, not mounted, thusconsiderably reducing the repair effort caused by mounting defectiveoptoelectronic semiconductor chips. It should also be mentioned herethat the interaction also depends on the mass or size of the μ-LEDs andmust therefore be selected accordingly for a nominal size so that afunctional μ-LED just sticks.

Alternatively, by appropriate design, μ-LEDs or optoelectronicsemiconductor chips with certain defects that reduce the dipole fieldcan be caused to be picked up by the pick-up tool and “good” μ-LEDs withhigher dipole fields can be rejected by the pick-up tool and remain onthe substrate. Such configuration also causes a separation of good anddefective μ-LEDs and optoelectronic semiconductor chips.

The pick-up tool can be made of a suitable material to generate anelectric field. For example, the pick-up tool may havepolydimethylsiloxane (PDMS) in which metal contacts are embedded. Themetal contacts can be connected to an electrical power source to chargethe PDMS material to generate the electric field. Furthermore, themounting tool can be made of a suitable electrically charged material,which generates an electric field by itself.

Another option for generating the electric field is to generate theelectric field, for example by contacts inside or on the surface of thepick-up tool and an electric voltage. The electric field can also extendbetween the pick-up tool and an electrical contact, with the μ-LEDslocated between the pick-up tool and the electrical contact. Theelectrical contact can, for example, be the carrier on which the μ-LEDsor optoelectronic semiconductor chips are placed or integrated into thecarrier.

The μ-LEDs can be produced on a semiconductor wafer and then separated,for example by sawing. After separation, the μ-LEDs can be mounted on acircuit board or other carrier using the method described here. It isalso possible to transfer not only individual μ-LEDs but also μ-LEDmodules or smaller arrays of contiguous μ-LEDs using this process. Inthis context, reference is made to the μ-LED modules or structuresdescribed in this application, which can be easily transferred using theproposed transfer method.

Due to their small dimensions and possibly large number, no conventionalmethods can be used economically for μ-LEDs, where the LEDs are firsttested and then mounted on a circuit board. Unlike conventional methods,the process described in the present application makes it possible tosort out defective μ-LEDs before mounting them.

The excitation of the μ-LEDs to generate the electron-hole pairs can beachieved by irradiating the μ-LEDs with light, especially UV light. Thelight spectrum must have a wavelength or a wavelength range that allowsexcitation, especially photoluminescence excitation. In particular, theexcitation radiation must have a higher energy than the radiationemitted by the optoelectronic semiconductor chips so that electron holepairs can be generated directly. Consequently, the wavelength of theexcitation radiation must be shorter than the wavelength of theradiation emitted by the optoelectronic semiconductor chips. Forexample, blue μ-LEDs emit light at about 460 nm. In this case, theexcitation radiation should have a wavelength of 440 nm or shorter, forexample a wavelength of approx. 420 nm.

The light used to generate the electron-hole pairs can fall on theμ-LEDs through the pick-up tool. To make this possible, the pick-up toolcan be made at least partially of a material that is at least partiallytransparent or translucent to the light. Furthermore, openings or lightguides can be integrated into the pick-up tool through which the lightreaches the μ-LEDs.

The μ-LEDs or semiconductor chips can be arranged on a carrier orsubstrate before being picked up by the pick-up tool. The light used togenerate the electron-hole pairs can pass through the carrier orsubstrate onto the μ-LEDs. For this purpose, the carrier or substratemay be made at least partially of a material that is at least partiallytransparent or transmissive to the light, or openings or light guidesmay be integrated into the carrier or substrate.

Alternatively, the light can be radiated laterally or at an angle ontothe μ-LEDs or all optoelectronic semiconductor chips.

It may be envisaged that electron-hole pairs are not generated in allμ-LEDs or optoelectronic semiconductor chips, but only selectively insome of the devices. For example, a plurality of μ-LEDs fabricated on awafer can be provided and the electron-hole pairs are only generated inselected μ-LEDs of the plurality of optoelectronic semiconductor chips.Then, except for the defective μ-LEDs of this selection, only theseμ-LEDs are picked up by the pick-up tool. The selective excitation ofthe μ-LEDs can be achieved, for example, by passing the light forgenerating the electron-hole pairs through a mask.

Another possibility for picking up only a selection of μ-LEDs is thatthe pick-up tool generates an electric field only in predeterminedareas. This can be achieved, for example, by at least partiallyindividually controlling the metal contacts embedded in the pick-uptool. By means of this selection it is possible to create suitabledistances of μ-LEDs to be recorded (e.g. only every third, fourth, tenthetc.). The distances can be selected in such a way that the recordedμ-LEDs can be placed directly on the target matrix.

According to one embodiment, the pick-up tool has a plurality ofprotrusions or stamps on a surface facing the μ-LEDs. When the pick-uptool is lowered, only the protrusions come into contact with theoptoelectronic semiconductor chips, so that only the protrusions pick upμ-LEDs. The areas between the elevations and the areas outside theelevations do not pick-up optoelectronic semiconductor chips. Here too,the elevations can be arranged at predefined distances corresponding tothe places to be occupied in a target matrix. In this application afurther concept is revealed, which continues this aspect.

Alternatively, at least in one area, the pick-up tool may have acontinuous flat surface intended for picking up the μ-LEDs. This allowsgreater flexibility, since μ-LEDs or optoelectronic semiconductor chipsarranged in different patterns and/or with different spacing can bepicked up.

Furthermore, the pick-up tool can have the shape of a cylinder, which isrolled over the μ-LEDs to pick up the μ-LEDs. For example, the pick-uptool can be shaped like the drum of a laser printer. To pick up theμ-LEDs, the cylindrical pick-up tool can be moved over the μ-LEDs.Alternatively, the axis of rotation of the cylindrical pick-up tool canbe stationary and the carrier with the optoelectronic semiconductorchips can be slid under the pick-up tool.

To deposit the μ-LEDs, the electrical charge of the pick-up tool can bechanged via the metal contacts. For example, the polarity of the metalcontacts can be reversed. This leads to a repulsive electricalinteraction between the pick-up tool and the μ-LEDs polarized by theelectron-hole pairs. As a result, the μ-LEDs either are noticed or hitthe target matrix.

Furthermore, the charge can also be changed only at certain positions orin certain areas of the pick-up tool, so that certain μ-LEDs areselectively deposited.

Another way of depositing the μ-LEDs is that the carrier or substrate towhich the μ-LEDs are applied generates an adhesive force that is greaterthan the attractive force between the pick-up tool and the μ-LEDs. Forexample, the surface of the carrier or substrate can be coated with anadhesive, a lacquer, a soldering material or other suitable materials.Furthermore, the μ-LEDs can be detached from the mounting tool bymechanical forces, for example by shearing or acceleration forces.

According to one embodiment, the pick-up tool directly touches theμ-LEDs or optoelectronic semiconductor chips to pick them up. During thetransfer of the optoelectronic semiconductor chips, the pick-up toolholds them by means of Van der Waals forces.

Another aspect concerns a device intended for picking up and placingoptoelectronic semiconductor chips. The device can be, for example, apick and place machine or be integrated into a pick and place machine.

The device comprises an excitation element for generating elec-tron-holepairs in μ-LEDs or optoelectronic semiconductor chips and a pick-up toolfor picking up and placing the μ-LEDs or optoelectronic semiconductorchips. The electron-hole pairs generate electrical dipole fields in thevicinity of the μ-LEDs or optoelectronic semiconductor chips. Thepick-up tool is configured in such a way that it generates an electricfield, which interacts with the electric dipole fields of the μ-LEDs, oroptoelectronic semiconductor chips in order to pick them up. The pickedup μ-LEDs or optoelectronic semiconductor chips are transferred topredetermined locations and deposited there.

According to one embodiment, the excitation element is designed togenerate light with a predetermined wavelength or a predeterminedwavelength range to generate the electron-hole pairs in the μ-LEDs oroptoelectronic semiconductor chips. The excitation element may, forexample, comprise a light source and/or a light guide.

The excitation element can be arranged in such a way that the light forgenerating the electron-hole pairs is incident on the μ-LEDs through thepick-up tool or through a carrier on which the μ-LEDs are arranged. Thepick-up tool may have a plurality of projections on a surface facing theμ-LEDs or the optoelectronic semiconductor chips. The μ-LEDs or theoptoelectronic semiconductor chips can be picked up by the projectionsof the pick-up tool.

Alternatively, at least a portion of a surface of the pick-up toolfacing the μ-LEDs or optoelectronic semiconductor chips may becontinuously flat and configured to receive the μ-LEDs or optoelectronicsemiconductor chips.

Furthermore, the device for picking up and depositing μ-LEDs oroptoelectronic semiconductor chips can have the above-describedconfigurations of the method for picking up and depositing μ-LEDs oroptoelectronic semiconductor chips.

A further aspect for the realization of μ-displays concerns a solutionin which a double transfer process is used for the transport andpositioning of μ-LEDs on a backplane substrate, wherein an intermediatecarrier is formed in the target size of the array, in particular thedisplay, and has an identical μ-LED density as the wafer on which theμ-LEDs are manufactured. During the transfer to the target substrate, athinning of the microchips is carried out, whereby in the best case themicro-chips of one color are transferred from the intermediate carrierto the target substrate by a correspondingly large transfer stamp in asingle transfer step per color red, green. An average number of transfersteps per array can be effectively reduced by more than one order ofmagnitude by means of such a two-stage transfer process. This results incost savings in the production of large area μ-displays by reducing thenumber of stamping steps by using an intermediate carrier

According to some aspects, a process for the production of a number (nor less) of arrays A of optoelectronic pixels, which are in particularμ-displays. The process can also be carried out for each of the colorsred, green and blue. In a first step, a large number of μ-LEDs with afirst density are generated on a wafer or carrier substrate. Then afirst transfer stamp is used to transfer the μ-LEDs to an intermediatecarrier with the first density. Then a second transfer step is performedby means of a second transfer stamp. This transfers the μ-LEDs from theintermediate carrier to a target substrate with a second density that isa factor n (n in particular an integer) smaller than the first density.The target substrate provides a common array surface for a respectiveone of the arrays, in particular for all three colors, the size of theintermediate carrier being equal to or larger than that of the secondtransfer stamp and the size of the second transfer stamp being equal toor smaller than the array surface by a factor k (k in particular aninteger).

In a further aspect, an intermediate carrier can be provided on whichmodule areas removed from the carrier substrate can be set down from thefirst transfer stamp. The intermediate carrier can have several moduleareas. In this way, an intermediate carrier is provided on which moduleareas can be temporarily transferred completely, but which can also beremoved again in a second transfer step in order to transfer to a finaltarget substrate.

The μ-LEDs on a carrier substrate can be manufactured in such a way thatthey can be removed from the carrier substrate individually or inparallel by means of anchor elements. The adhesive force on theintermediate carrier must be stronger than the adhesive force of theμ-LEDs on the first transfer stamp. If the μ-LEDs are removed from theintermediate carrier for a second time, the adhesive force of the μ-LEDson the second transfer stamp must be correspondingly greater than theadhesive force on the intermediate carrier. Likewise, the transfer fromthe second transfer stamp to the final substrate surface must bepossible by a suitable choice of adhesive, intervias or soldering on thetarget substrate. The coordination of adhesive and release forces by asuitable material selection and a suitable process control for the twostamping processes leads to the provision of a starting structure.

For this purpose, the system proposes a start structure that uses atwo-level use of anchor elements. On the one hand, anchor elements areused for entire module areas on which many thousands or many millions ofμ-LEDs are arranged. Secondly, anchor elements are used for the transferof μ-LEDs from the intermediate carrier to the target substrate.

According to another aspect, when creating the μ-LEDs, they can becreated together with the respective module areas, which can each beconnected to the carrier substrate. According to a further embodiment,when generating the μ-LEDs, first anchor elements for connecting with afirst adhesive force can be formed between the module areas and thewafer and/or second anchor elements for connecting with a secondadhesive force can be formed between the μ-LEDs and the module areas.

A further aspect concerns the lift-off force. A lift-off force is aforce that must be applied at least to perform a lift-off. For example,when performing the first transfer steps, the lifting force of thelifting first transfer die can be set to be greater than the firstadhesive force and less than the second adhesive force so that themodule areas can be lifted off the wafer and transferred to theintermediate carrier. Correspondingly, it is conceivable in a furtheraspect that, when carrying out the second transfer steps, the liftingforce of the lifting second transfer stamp is set greater than thesecond adhesive force in such a way that the microchips can be liftedoff the module areas and transferred to the target substrate.

In another aspect, release elements are formed between wafer and moduleareas and/or between μ-LEDs and module areas in such a way that aftertheir removal, a first and/or a second defined adhesive force is set ineach case. It is also conceivable that when generating the μ-LEDsbetween the module areas and the wafer, additional first releaseelements for connecting with an additional first adhesive force and/orbetween the microchips and the module areas, additional optional secondrelease elements for connecting with an additional second adhesive forceare formed.

According to another embodiment, when carrying out the first transfersteps, the lifting force of the lifting first transfer die can be set tobe greater than the total first adhesive force and less than the totalsecond adhesive force so that the module areas can be lifted off thewafer and transferred to the intermediate carrier. Alternatively oradditionally, when carrying out the second transfer steps, the liftingforce of the lifting second transfer stamp can be set to be greater thanthe total second adhesive force so that the microchips can be lifted offthe module areas and transferred to the target substrate.

In a further aspect of this, the additional second adhesive force can bereduced to zero by removing the second release elements beforehand. Inthis way, the lifting force of the lifting second transfer stamp neednot be greater than the lifting force of the lifting first transferstamp.

According to another embodiment, materials with a greater adhesive forcethan the second defined adhesive force can be used to carry out thesecond transfer step for the adhesion of the module areas to theintermediate carrier. The second adhesive force is set accordingly forthe second transfer step using separate anchor elements and, ifnecessary, release elements. It is conceivable to form lifting elementsdirectly on the module areas for lifting and transferring the moduleareas to the intermediate carrier in order to carry out the firsttransfer step.

A further aspect deals with the correct positioning of the module areason the intermediate carrier or even the target substrate. In one aspectof this, positioning elements are formed directly on the module areas tocarry out the first transfer steps for the precise transfer of themodule areas to the intermediate carrier. These positioning elementsserve as orientation for the first transfer stamp. The positioningelements can be provided by means of the lifting elements.

According to another embodiment, for the execution of the secondtransfer steps, tapping elements can be formed on the second transferdie for thinning out the μ-LEDs into the second density. The density ofthese elements corresponds to the second density of a display.

According to another aspect, the size of the rectangular first transferdie can be chosen smaller by a factor of s to the size of the roundcarrier substrate in such a way that the size of an area of lost μ-LEDsat the edge of the carrier substrate for the first transfer tocompletely fill the receiving area is small, in particular per colorless than or equal to 20% or less than or equal to 30% of the carriersubstrate area. Alternatively, the size of the rectangular firsttransfer stamp can be selected to be smaller than the size of theintermediate carrier by a factor r in such a way that the number offirst transfer steps r for the first transfer for complete loading ofthe intermediate carrier is small, in particular per color less than orequal to 10 or less than or equal to 50.

According to another embodiment, the shape of the intermediate carriercan correspond to the shape of the second transfer stamp and this inparticular to the shape of the array surface. The shape of the array ofoptoelectronic pixels can be rectangular, trapezoidal, triangular orpolygonal, have rounded corners, or be any other free form. According toanother embodiment, the intermediate carrier can be equipped with testedmodule areas from one carrier substrate or from different carriersubstrates. According to another embodiment, the distances between theμ-LEDs on the respective wafer can correspond to the distance betweenthe μ-LEDs on the intermediate carrier.

According to a further embodiment, the distances between μ-LEDs on arespective intermediate carrier and on a respective target substrate inan x-direction can be different from those in a y-direction. Accordingto another embodiment, the target substrate can be equipped with moduleareas of several intermediate carriers.

According to another embodiment, the color of the microchips of arespective intermediate carrier can be monochrome red, green or blue andthe number of n color arrays can be formed from three intermediatecarriers, which have microchips of different colors to each other.

According to another embodiment, first first release elements can beselectively removed between wafer and module areas and then secondrelease elements between microchips and module areas.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following section, some of the above-mentioned and summarizedaspects are explained in more detail using various explanations andexamples.

FIG. 1A shows a diagram illustrating some requirements for so-calledμ-displays or micro-displays of different sizes with respect to thefield of view and pixel pitch of the μ-display;

FIG. 1B shows a diagram of the spatial distribution of rods and cones inthe human eye;

FIG. 1C shows a diagram of the perceptual capacity of the human eye withassigned projection areas;

FIG. 1D is a figure showing the sensitivity of the rods and cones overthe wavelength;

FIG. 2A is a diagram illustrating some requirements for micro-displaysof different sizes in terms of the field of view and the angle ofcollimation of a pixel of the μ-display;

FIG. 2B illustrates an exemplary execution of a pixel arrangement toillustrate the parameters used in FIGS. 1A and 2A;

FIG. 3A shows a diagram illustrating the number of pixels requireddepending on the field of view for a specific resolution;

FIG. 3B is a table of preferred applications for μ-LED arrays;

FIG. 4A shows a principle representation of a μ-LED display withessential elements for light generation and light guidance;

FIG. 4B shows a schematic representation of a μ-LED array with similarμ-LEDs;

FIG. 4C is a schematic representation of a μ-LED array with μ-LEDs ofdifferent light colors;

FIG. 5 shows a simplified structure of a display with pixel elementsarranged in rows and columns;

FIG. 6 shows an enlarged section of a display according to the previousfigure with one pixel element and subpixels;

FIG. 7 shows a schematic vertical sectional view through a section of adisplay according to the proposed concept with a pixel elementseparation layer and subpixel separation elements;

FIG. 8 illustrates a schematic vertical sectional view through pixelelements applied in a layer on a backplane;

FIG. 9 is an embodiment where various converters are embedded in alight-shaping structure;

FIG. 10 illustrates another aspect where quantum well intermixing isused to create an optical separation;

FIG. 11 shows steps of a method for calibrating a pixel element with apixel element separation layer and sub-pixel separation elements;

FIG. 12 shows a first embodiment of a pixel array according to someaspects of the proposed principle, where adjacent pixels are connectedby a thin material bridge;

FIG. 13 shows a second embodiment of a pixel array with two μ-LEDsconnected by a material bridge;

FIG. 14A is a third embodiment of a pixel array with some aspectsaccording to the proposed principle;

FIG. 14B is a diagram for the embodiment of the previous figure, whichillustrates the energy flow with regard to the material bridge;

FIG. 15 shows a fourth embodiment of a pixel array with some aspectsaccording to the proposed principle;

FIG. 16A is a fifth embodiment of a pixel array;

FIG. 16B shows an embodiment of a pixel array with adjacent μ-LEDs, amaterial bridge, with an additional output structure according to someof the aspects revealed here.

FIG. 17 shows a sixth embodiment of a pixel array;

FIG. 18 is a seventh embodiment of a pixel array with further aspects;

FIG. 19 shows an eighth embodiment of a pixel array;

FIG. 20 shows a ninth embodiment of a pixel array;

FIG. 21 shows an embodiment with different steps for a method ofmanufacturing a pixel array according to the proposed concept;

FIGS. 22A to 22J show a first embodiment of a process for manufacturinga μ-LED with a holding structure according to some aspects of thepresented concept;

FIGS. 23A to 23J show a second embodiment of a process for manufacturinga μ-LED with a holding structure according to some aspects of thepresented concept;

FIGS. 24A to 24I represent a third embodiment of a process formanufacturing a μ-LED with a holding structure according to some aspectsof the concept presented;

FIGS. 25A to 25J show a fourth embodiment of a process for manufacturinga μ-LED with a holding structure according to some aspects of thepresented concept;

FIGS. 26A and 26B represent two additional steps that can be used in thevarious embodiment;

FIGS. 27A to 27D show the schematic sequence of a mass transfer printingprocess for a large number of μ-LEDs on a wafer;

FIG. 28 shows a support structure according to the proposed principle ina top view with 3 mounting elements;

FIGS. 29A to 29E show a total of four vertical sectional views through acarrier structure for holding flat μ-LEDs suitable for the proposedtransfer;

FIG. 30 shows a layout of a carrier structure according to some aspectsof the proposed concept with flat μ-LEDs and a variety of mountingelements in different arrangements;

FIG. 31 shows another layout of a support structure, prepared andsuitable for the proposed transfer process;

FIG. 32A shows another embodiment of a support structure;

FIG. 32B is an alternative to the previous embodiment;

FIGS. 33A to 33D are illustrations of a process and a device for pickingup and placing μ-LEDs or optoelectronic semiconductor chips to explainvarious aspects of the concept presented;

FIG. 34 shows a representation of another device for picking up andplacing μ-LEDs or optoelectronic semiconductor chips;

FIGS. 35A and 35B show illustrations of an embodiment of a process forpicking up and placing μ-LEDs or optoelectronic semiconductor chipsusing a cylindrical pick-up tool;

FIG. 36 illustrates an illustration of a pick-up tool with elevationsfor picking up μ-LEDs or optoelectronic semiconductor chips;

FIG. 37 shows a version of a pick-up tool that is suitable for selectiveirradiation of μ-LEDs or optoelectronic semiconductor chips;

FIG. 38 illustrates a representation of a pick-up tool with a flatsurface for picking up μ-LEDs or optoelectronic semiconductor chips;

FIGS. 39A through 39C show illustrations of a method for depositingμ-LEDs; and

FIGS. 40A to 40C are different representations of some of the ways inwhich an electric field is generated by the pick-up tool;

FIGS. 41A and 41B show illustrations showing transfer steps of aconventional method and the proposed method;

FIG. 42 is a first embodiment of a start structure for a procedureaccording to some suggested aspects in a top view;

FIG. 43 shows the first embodiment according to FIG. 42 of the startstructure for the procedure in an enlarged view;

FIG. 44 shows a further illustration for a manufacture of a first startstructure according to some of the proposed aspects;

FIG. 45 is an embodiment of the inventive step with some aspects of theproposed principle;

FIG. 46 shows the first embodiment of the start structure for aprocedure in a cross-section;

FIGS. 47A to 47E show a further embodiment of an invention-relatedprocedure using a first start structure;

FIG. 48 is a first illustration of the mode of action of anchor elementsand release elements according to some aspects presented;

FIG. 49 is a second illustration of how anchor elements and releaseelements work;

FIG. 50 shows a second embodiment of a starting structure for a transferprocedure according to some suggested aspects;

FIGS. 51A to 51E show another embodiment of a proposed procedure usingthe second start structure;

FIG. 52A is a first illustration of the selectivity of release elementsaccording to some aspects of the proposed concept for a transfer;

FIG. 52B shows a second illustration of the selectivity of releaseelements;

FIGS. 53A to 53F show examples of the use of anchor elements and releaseelements between microchips and module areas;

FIG. 54 shows an illustration of an embodiment of a proposed base modulefor the provision of light emitting diode modules according to someaspects of the proposed concept;

FIG. 55 shows the embodiment according to FIG. 54 on a replacementcarrier according to further aspects;

FIG. 56 illustrates the embodiment according to FIG. 55 with a furtherbasic module;

FIG. 57 shows the embodiment according to FIG. 56 with separatecontacting of the contacts;

FIG. 58 illustrates the embodiment according to FIG. 57 with commoncontacting of the first contacts;

FIG. 59 shows a further illustration of an embodiment of a proposed basemodule to provide a two row and two column light emitting diode moduleaccording to some aspects of the concept presented;

FIGS. 60A to 60D show four cross sections of two oppositely orientedbase modules of two adjacent rows;

FIG. 61 shows a further illustration of an embodiment of a proposed basemodule to provide a two row and three column light emitting diodemodule;

FIG. 62A to 62D illustrate four cross sections of two oppositelyoriented base modules of two adjacent rows;

FIG. 63 shows a top view of a matrix containing basic modules withgroupings to explain further aspects;

FIG. 64 illustrates a top view of a matrix with basic modules andfurther groupings;

FIG. 65 shows a top view of a matrix with basic modules and anotherpossible grouping;

FIG. 66 is a top view of a matrix with basic modules and anotherpossible grouping;

FIG. 67A illustrates a cross-sectional view of another embodiment of aμ-LED module with an additional photonic structure;

FIG. 67B shows an example of how the proposed μ-LED module can be liftedoff by a transfer stamp described in this application;

FIG. 68 shows several steps of an embodiment of a proposed process formanufacturing μ-LED modules;

FIG. 69 illustrates a schematic representation of another method for theproduction of μ-LED modules according to some aspects of the proposedprinciple;

FIG. 70A are illustrations of some steps of the method presented in FIG.69;

FIG. 70B shows an illustration of further steps of the method presentedin FIG. 69 for an explanation of various aspects;

FIG. 70C shows a representation of an arrangement of a large number offull-surface target matrices;

FIG. 70D illustrates schematically various contact surfaces that aresuitable for contacting the proposed μ-LED modules;

FIG. 70E shows a section of a display with contact areas and some μ-LEDmodules;

FIG. 71 shows an embodiment for a double transfer process with proposedμ-LED modules;

FIG. 72 shows a first embodiment of a μ-LED module for vertical andhorizontal mounting with some aspects according to the proposedprinciple;

FIG. 73 shows the bottom of the first embodiment;

FIG. 74 shows a sectional view of the first embodiment along the X-Xaxis in FIG. 73;

FIG. 75 shows another embodiment of a μ-LED module for vertical andhorizontal mounting with some aspects according to the proposedprinciple;

FIG. 76 shows a schematic side view of FIG. 75;

FIGS. 77A to 77C show various embodiments in which a module is placed ona carrier and electrically contacted;

FIG. 78A and 78B show a second embodiment with some aspects according tothe proposed principle;

FIG. 79A and 79B shows a third embodiment with some aspects according tothe proposed principle;

FIG. 80 shows an embodiment with different process steps;

FIG. 81 shows a first embodiment of a contacting in perspective;

FIG. 82A and 82B shows two top views with a schematic wiring diagram fora module based on the proposed principle;

FIG. 83 shows a view of a bottom side of the above embodiments;

FIG. 84 shows an example of a structured membrane wafer during themanufacturing process of a module according to the proposed principle;

FIG. 85A is a top view of the contacts of a substrate in an unpopulatedstate provided for a pixel according to an aspect of the proposedconcept;

FIG. 85B shows a top view of the contacts of the substrate of

FIG. 85A provided for the pixel after an initial assembly of μ-LEDs;

FIG. 85C shows a top view of the contacts of the substrate of FIG. 85Aprovided for the pixel after a second assembly of μ-LEDs;

FIG. 86A illustrates a top view of the contacts of another substrate inan unpopulated state, provided for one pixel;

FIG. 86B is a top view of the contacts of the substrate of FIG. 86Aprovided for the pixel after an initial placement;

FIG. 86C shows a top view of the contacts of the substrate of FIG. 86Aprovided for the pixel after a second placement;

FIG. 87A shows a top view of the contacts provided for one pixel of yetanother substrate in an unpopulated state to illustrate further aspectsof the proposed concept;

FIG. 87B shows a top view of the contacts of the substrate of FIG. 82Aprovided for the pixel after an initial placement; and

FIG. 87C is a top view of the contacts of the substrate of

FIG. 82A provided for the pixel after a second placement.

DETAILED DESCRIPTION

Augmented reality is usually generated by a dedicated display whoseimage is superimposed on reality. Such device can be positioned directlyin the user's line of sight, i.e. directly in front of it.Alternatively, optical beam guidance elements can be used to guide thelight from a display to the user's eye. In both cases, the display maybe implemented and be part of the glasses or other visually enhancingdevices worn by the user. Google's™ Glasses is an example of such avisually augmenting device that allows the user to overlay certaininformation about real world objects. For the Googlem glasses, theinformation was displayed on a small screen placed in front of one ofthe lenses. In this respect, the appearance of such an additional deviceis a key characteristic of eyeglasses, combining technical functionalitywith a design aspect when wearing glasses. In the meantime, usersrequire glasses without such bulky or easily damaged devices to provideadvanced reality functionality. One idea, therefore, is that the glassesthemselves become a display or at least a screen on or into which theinformation is projected.

In such cases, the field of vision for the user is limited to thedimension of the glasses. Accordingly, the area onto which extendedreality functionality can be projected is approximately the size of apair of spectacles. Here, the same, but also different information canbe projected on, into or onto the two lenses of a pair of spectacles.

In addition, the image that the user experiences when wearing glasseswith augmented reality functionality should have a resolution thatcreates a seamless impression to the user, so that the user does notperceive the augmented reality as a pixelated object or as alow-resolution element. Straight bevelled edges, arrows or similarelements show a staircase shape that is disturbing for the user at lowresolutions.

In order to achieve the desired impression, two display parameters areconsidered important, which have an influence on the visual impressionfor a given or known human sight. One is the pixel size itself, i.e. thegeometric shape and dimension of a single pixel or the area of 3subpixels representing the pixel. The second parameter is the pixelpitch, i.e. the distance between two adjacent pixels or, if necessary,subpixels. Sometimes the pixel pitch is also called pixel gap. A largerpixel pitch can be detected by a user and is perceived as a gap betweenthe pixels and in some cases causes the so-called fly screen effect. Thegap should therefore not exceed a certain limit.

The maximum angular resolution of the human eye is typically between0.02 and 0.03 angular degrees, which roughly corresponds to 1.2 to 1.8arc minutes per line pair. This results in a pixel gap of 0.6-0.9 arcminutes. Some current mobile phone displays have about 400 pixels/inch,resulting in a viewing angle of approximately 2.9° at a distance of 25cm from a user's eye or approximately 70 pixels/° viewing angle and cm.The distance between two pixels in such displays is therefore in therange of the maximum angular resolution. Furthermore, the pixel sizeitself is about 56 μm.

FIG. 1A illustrates the pixel pitch, i.e. the distance between twoadjacent pixels as a function of the field of view in angular degrees.In this respect, the field of view is the extension of the observableworld seen at a given moment. This is because human vision is defined asthe number of degrees of the angle of view during stable fixation of theeye.

In particular, humans have a forward horizontal arc of their field ofvision for both eyes of slightly more than 210°, while the vertical arcof their field of vision for humans is around 135°. However, the rangeof visual abilities is not uniform across the field of vision and canvary from person to person. The binocular vision of humans coversapproximately 114° horizontally (peripheral vision), and about 90°vertically. The remaining degrees on both sides have no binocular areabut can be considered part of the field of vision.

Furthermore, color vision and the ability to perceive shapes andmovement can further limit the horizontal and vertical field of vision.The rods and cones responsible for color vision are not evenlydistributed.

This point of view is shown in more detail in FIGS. 1B to 1D. In thearea of central vision, i.e. directly in front of the eye, as requiredfor Augmented Reality applications and partly also in the automotivesector, the sensitivity of the eye is very high both in terms of spatialresolution and in terms of color perception.

FIG. 1B shows the spatial density of rods and cones per mm² as afunction of the fovea angle. FIG. 1C describes the color sensitivity ofcones and rods as a function of wavelength. In the central area of thefovea, the increased density of cones (L, S and M) means that bettercolor vision predominates. At a distance of about 25° around the fovea,the sensitivity begins to decrease and the density of the visual cellsdecreases. Towards the edge, the sensitivity of color vision decreases,but at the same time contrast vision by means of the rods remains over alarger angular range. Overall, the eye develops a radially symmetricalvisual pattern rather than a Cartesian visual pattern. A high resolutionfor all primary colors is therefore required, especially in the center.At the edge it may be sufficient to work with an emitter adapted to thespectral sensitivity of the rods (max. sensitivity at 498 nm, see FIG.1D and the sensitivity of the eye).

FIG. 1C shows the different perceptual capacity of the human eye bymeans of a graph of the angular resolution A relative to the angulardeviation a from the optical axis of the eye. It can be seen that thehighest angular resolution A is in an interval of the angular deviationα of +/−2.5°, in which the fovea centralis 7 with a diameter of 1.5 mmis located on the retina 19. In addition, the position of the blind spot22 on the retina 19 is sketched, which is located in the area of theoptic nerve papilla 23, which has a position with an angular deviation aof about 15°.

The eye compensates this non-constant density and also the so-calledblind spot by small movements of the eye. Such changes in the directionof vision or focus can be counteracted by suitable optics and trackingof the eye.

Furthermore, even with glasses, the field of vision is furtherrestricted and, for example, can be approximately in the range of 80°for each lens.

The pixel pitch in FIG. 1A on the Y-axis is given in μm and defines thedistance between two adjacent pixels. The various curves C1 to C7 definethe diagonal dimension of a corresponding display from 5 mm toapproximately 35 mm. For example, curve C1 corresponds to a display withthe diagonal size of 5 mm, i.e. a side length of approximately 2.25 mm.For a field of view of approximately 80°, the pixel pitch of a displaywith a diagonal size of 5 mm is in the range of 1 μm. For largerdisplays like curve C7 and 35 mm diagonal size, the same field of viewcan be implemented with a pixel pitch of approximately 5 μm.

Nevertheless, the curves in FIG. 1A illustrate that for larger fields ofview, which are preferred for extended reality applications, very highpixel densities with small pixel pitch are required if the well-knownfly screen effect is to be avoided.

One can now calculate the size of the pixel for a given number ofpixels, a given field of view and a given diagonal size of a μ-display.

Equation 1 shows the relationship between dimension D of a pixel, pixelpitch pp, number N of pixels and the edge length d of the display. Thedistance r between two adjacent pixels calculated from their respectivecenters is given by

r=d/2+pp+d/2.

D=d/N−pp

N=d/(D+pp)   (1)

Assuming that the display (e.g. glasses) is at a distance of 2.54 cm (1inch) from the eye, the distance r between two adjacent pixels for anangular resolution of 1 arcminute as roughly estimated above is given by

r=tan(1/60°)*30 mm

r=8.7 μm

The size of a pixel is therefore smaller than 10 μm, especially if somespace is required between two different pixels. With a distance, rbetween two pixels and a display with the size of 15 mm×10 mm, 1720×1150pixels can be arranged on the surface.

FIG. 2B shows an arrangement, which has a carrier 21 on which a largenumber of pixels, 20 and 20 a to 20 c are arranged. Pixels 20 arrangedside by side have the pixel pitch pp, while pixels 20 a to 20 c areplaced on carrier 21 with a larger pixel pitch pp. The distance betweentwo pixels is given by the sum of the pixel pitch and half the size foreach adjacent pixel. Each of the pixels 20 is configured so that itsillumination characteristic or its emission vector 22 is substantiallyperpendicular to the emission surface of the corresponding LED.

The angle between the perpendicular axes to the emission surface of theLED and the beam vector is defined as the collimation angle. In theexample of emission vector 22, the collimation angle of LEDs 20 isapproximately zero. LED 20 emits light that is collinear and does notwiden significantly.

In contrast, the collimation angle of the emission vector 23 of the LEDpixels 20 a to 20 c is quite large and in the range of approximately45°. As a result, part of the light emitted by LED 20 a overlaps withthe emission of an adjacent LED 20 b.

The emission of the LEDs 20 a to 20 c is partially overlapping, so thatits superposition of the corresponding light emission occurs. In casethe LEDs emit light of different colors, the result will be a colormixture or a combined color. A similar effect occurs between areas ofhigh contrast, i.e. when LED 20 a is dark while LED 20 b emits a certainlight. Because of the overlap, the contrast is reduced and informationabout each individual position corresponding to a pixel position isreduced.

In displays where the distance to the user's eye is only small, as inthe applications mentioned above, a larger collimation angle is ratherannoying due to the effects mentioned above and other disadvantages. Auser is able to see a wide collimation angle and may perceive displayedobjects in slightly different colors blurred or with reduced contrast.

FIG. 2A illustrates in this respect the requirement for the collimationangle in degrees against the field of view in degrees, independent ofspecific display sizes. For smaller display sizes such as the one incurve C1 (approx. 5 mm diagonal), the collimation angle increasessignificantly depending on the field of view.

As the size of the display increases, the collimation angle requirementschange drastically, so that even for large display geometries such asthose illustrated in curve C7, the collimation angle reaches about 10°for a field of view of 100°. In other words, the collimation anglerequirements for larger displays and larger fields of view areincreasing. In such displays, light emitted by a pixel must be highlycollimated to avoid or reduce the effects mentioned above. Consequently,strong collimation is required when displays with a large field of vieware to be made available to a user, even if the display geometry isrelatively large.

As a result of the above diagrams and equations, one can deduce that therequirements regarding pixel pitch and collimation angle becomeincreasingly challenging as the display geometry and field of view grow.As already indicated by equation 1, the dimension of the displayincreases strongly with a larger number of pixels. Conversely, a largenumber of pixels is required for large fields of view if sufficientresolution is to be achieved and fly screens or other disturbing effectsare to be avoided.

FIG. 3A shows a diagram of the number of pixels required to achieve anangular resolution of 1.3 arc minutes. For a field of view ofapproximately 80°, the number of pixels exceeds 5 million. It is easy toestimate that the size of the pixels for a QHD resolution is well below10 μm, even if the display is 15 mm×10 mm. In summary, advanced realitydisplays with resolutions in the HD range, i.e. 1080 p, require a totalof 2.0736 million pixels. This allows a field of view of approximately50° to be covered. Such a quantity of pixels arranged on a display sizeof 10×10 mm with a distance between the pixels of fpm results in a pixelsize of about 4 μm.

In contrast, the table in FIG. 3B shows several application areas inwhich μ-LED arrays can be used. The table shows applications (use case)of μ-LED arrays in vehicles (Auto) or for multimedia (MM), such asautomotive displays and exemplary values regarding the minimum andmaximum display size (min. and max. size X Y [cm]), the pixel density(PPI) and the pixel pitch (PP [μm]) as well as the resolution(Res.-Type) and the distance of the viewer (Viewing Distance [cm]) tothe lighting device or display. In this context, the abbreviations “verylow res”, “low res”, “mid res” and “high res” have the followingmeaning:

very low res pixel pitch approx. 0.8-3 mm low res Pixel pitch approx.0.5-0.8 mm mid res Pixel pitch approx. 0.1-0.5 mm high res Pixel pitchless than 0.1 mm

The upper part of the table, entitled “Direct Emitter Displays”, showsinventive applications of μ-LED arrays in displays and lighting devicesin vehicles and for the multimedia sector. The lower part of the table,titled “Transparent Direct Emitter Displays”, names various applicationsof μ-LED arrays in transparent displays and transparent lightingdevices. Some of the applications of μ-displays listed in the table areexplained in more detail below in the form of embodiments.

The above considerations make it clear that challenges are considerablein terms of resolution, collimation and field of view suitable forextended reality applications. Accordingly, very high demands are placedon the technical implementation of such displays.

Conventional techniques are configured for the production of displaysthat have LEDs with edge lengths in the range of 100 μm or even more.However, they cannot be automatically scaled to the sizes of 70 μm andbelow required here. Pixel sizes of a few pm as well as distances of afew μm or even less come closer to the order of magnitude of thewavelength of the generated light and make novel technologies inprocessing necessary.

In addition, new challenges in light collimation and light direction areemerging. Optical lenses, for example, which can be easily structuredfor larger LEDs and can also be calculated using classical optics,cannot be reduced to such a small size without the Maxwell equations.Apart from this, the production of such small lenses is hardly possiblewithout large errors or deviations. In some variants, quantum effectscan influence the behaviour of pixels of the above-mentioned size andhave to be considered. Tolerances in manufacturing or transfertechniques from pixels to sub mounts or matrix structures are becomingincreasingly demanding. Likewise, the pixels must be contacted andindividually controllable. Conventional circuits have a spacerequirement, which in some cases exceeds the pixel area, resulting in anarrangement and space problem.

Accordingly, new concepts for the control and accessibility of pixels ofthis size can be quite different from conventional technologies.Finally, a focus is on the power consumption of such displays andcontrollers. Especially for mobile applications, a low power consumptionis desirable.

In summary, for many concepts that work for larger pixel sizes,extensive changes must be made before a reduction can be successful.While concepts that can be easily up scaled to LEDs at 2000 μm for theproduction of LEDs in the 200 μm range, downscaling to 20 μm is muchmore difficult. Many documents and literature that disclose suchconcepts have not taken into account the various effects and increaseddemands on the very small dimensions and are therefore not directlysuitable or limited to pixel sizes well above 70 μm.

In the following, various aspects of the structure and design of μ-LEDsemiconductors, aspects of processing, light extraction and lightguidance, display and control are presented. These are suitable anddesigned to realize displays with pixel sizes in the range of 70 μm andbelow. Some concepts are specifically designed for the production, lightextraction and control of μ-LEDs with an edge length of less than 20 μmand especially less than 10 μm. It goes without saying, and is evendesired, that the concepts presented here can and should be combinedwith each other for the different aspects. This concerns for example aconcept for the production of a μ-LED with a concept for lightextraction. In concrete terms, a μ-LED implemented by means of methodsto avoid defects at edges or methods for current conduction or currentconstriction can be provided with light extraction structures based onphotonic crystal structures. Likewise, a special drive can also berealized for displays whose pixel size is variable. Light guidance withpiezoelectric mirrors can be realized for μ-LEDs displays based on theslot antenna aspect or on conventional monolithic pixel matrices.

In some of the following embodiments and described aspects, additionalexamples of a combination of the different embodiments or individualaspects thereof are suggested. These are intended to illustrate that thevarious aspects, embodiments or parts thereof can be combined with eachother by the skilled person. Some applications require specially adaptedconcepts; in other applications, the requirements for the technology aresomewhat lower. Automotive applications and displays, for example, mayhave a longer pixel edge length due to the generally somewhat greaterdistance to a user. Especially there, besides applications of extendedreality, classical pixel applications or virtual reality applicationsexist. This is in the context of this disclosure for the realization ofμ-LED displays, whose pixel edge length is in the range of 70 μm andbelow, also explicitly desired.

A general illustration of the main components of a pixel in a μ-displayis shown schematically in FIG. 4A. It shows an element 60 as a lightgenerating and light emitting device. Various aspects of this aredescribed in more detail below in the section on light generation andprocessing. Element 60 also includes basic circuits, interconnects, andsuch to control the illumination, intensity, and, when applicable, colorof the pixel. Aspects of this are described in more detail in thesection on light control. Apart from light generation, the emitted lightmust be collimated. For this purpose, many pixels in microdisplays havesuch collimation functionality in element 60. The parallel light inelement 63 is then fed for light guidance into some optics 64, forfurther shaping and the like. Light collimation and optics suitable forimplementing pixels for microdisplays are described in the section onlight extraction and light guidance.

The pixel device of FIG. 4A illustrates the different components andaspects as separate elements. An expert will recognize that manycomponents can be integrated into a single device. In practice, theheight of a μ-display is also limited, resulting in a desired flatarrangement.

The following section concern various aspects of processing a μ-LED,which can be used to improve the electrical or optical properties or tocreate new fields of application or realization possibilities. It goeswithout saying that μ-LEDs come in different forms, structures andfeatures. Some of those aspects are disclosed in the previous mentinedPCT-application, the disclosure of which is incorporated herein. Theμ-LED are in some aspects implemented in a monolitical way, in otheraspects a μ-LED or a few μ-LED form a pixel which are subsequentlyprocessed individually. As outlined herein, the various aspects ofprocessing aim to improve the characteristics of the semiconductorstructure or simplify the transfer.

For illustrating the aspect of pixel elements with electricallyseparated and optically coupled subpixels a simplified schematic diagramof an electronic display 10 is shown in FIG. 5, as it is often used in,for example, monitors, televisions, scoreboards or even small devicessuch as smart watches or smart phones. As is generally known, the basicstructure is realized by a closely adjacent arrangement of a largenumber of pixels or pixel elements 12 in one plane. The pixel elements12 are organized in rows and columns and can be controlledelectronically individually. They are controlled in such a way that theycan be varied in their luminosity as well as in their color tone andemitted wavelength. In the latter case, each pixel often comprises threesub-pixels, which in turn are designed to emit different wavelengths.The pixel elements 12 are often mounted on a substrate or carrierstructure 14, which in this aspect are primarily intended to ensuremechanical stability of the arrangement.

This illustration shows clearly that in order to generate a sufficientlyhigh resolution, several million of such pixel elements 12 must bespatially densely arranged both mechanically and electrically. At thesame time, in many cases defective pixels 12 can be detected as darkdots between the active pixels. Especially due to extremely smalldimensions, e.g. for μ-LEDs, the density and resolution of such displaysincreases on the one hand, while on the other hand there is a need forfault-free operation and production with as few rejects as possible.

In FIG. 6, the section AA shown in FIG. 5 is enlarged in order to beable to describe the features of the solution in more detail. Forexample, substrate 14 is shown to simultaneously contain the controlelements and serve as a support structure for the pixels. On substrate14, individual pixel elements 12 are provided, which here arerectangular and of the same size. These identical sizes of the pixelelements 12 are often advantageous for manufacturing reasons, but canalso be designed in different shapes or sizes according to an example.The pixel element 12 in the example shown here has a length 11 and awidth b1. A pixel element separation layer 16 is provided between thepixel elements 12. The latter is in the range of a few μm, for example0.5 μm to 3 μm.

The pixel element separation layer 16 is configured in such a way thatthe adjacent pixel elements 12 are electrically separated with respectto the control of the respective pixel elements. FIG. 7 shows a sectionof a pixel element in cross-sectional view. The pixel elements 12 areseparated by a pixel element separation layer 16 and each comprisessub-pixels 18. The pixel element separation layer 16 provides electricaland optical separation between the pixel elements 12. This is intendedto prevent light emitted by a pixel element 12 from passing throughoptical crosstalk into an adjacent pixel element 12 and being emittedfrom there.

Within a pixel element 12, a further subdivision into subpixels 18 isshown here, as an example of a selected pixel element 12. The subpixels18, also known as fields, have the same size and shape here. A length 12of a subpixel 18 is defined, whereby, according to an example, thelength 11 of the pixel element 12 can result from a multiple of thelength 12 of the subpixels 12 of the same size including any gaps.Similarly, a width b2 of a subpixel is specified, where, according to anexample, the width bl of the pixel element can also result from anapproximate multiple of the width b 2 of the respective equally sizedsubpixels 18 including any gaps. The representation selected here showsthe subdivision of pixel element 12 into subpixels 18 or so-calledfields for only one pixel element 12. However, the structuring isapplicable to all pixel elements 12 arranged in a display 10.

Between two adjacent subpixels 18 of the same pixel element 12 asubpixel separator element 20 is also provided. This subpixel separatingelement 20 is configured in such a way that electrical separation takesplace with respect to the control of an assigned subpixel (of length 12)(see FIG. 7). The subpixel separating element 20 is further configuredin such a way that optical coupling or optical crosstalk is possiblewith respect to the light emitted by the subpixels 18. In other words,this means that within a pixel element 12 photons or light can crosstalk from a subpixel 18 to one or more of the subpixels 18 located inthe same pixel element 12, but not between two pixel elements 12.

For example, the various possible emittable colors of a pixel element 12can be generated by combining the basic colors red, green and blue.Consequently, a pixel element 12 can contain subpixels 18, which canemit different wavelengths of light. In FIG. 6, for example, the totalof nine subpixels 18 are marked with the letters A to K. According toone example, the subpixels A, D, and G are red LEDs, the subpixels B, E,and H are green LEDs, and the subpixels C, F, and K are blue LEDs. If,for example, red light is to be emitted by pixel element 12, thesubpixels A, D and G are controlled simultaneously via the controlelectronics. If necessary, the control electronics can be used to testwhether all subpixels A, D and G are functioning correctly. By thismeans, a desired brightness can be adjusted.

If, for example, one of the subpixels A, D or G is defective, theremaining pixels can still be controlled correctly due to the electricalseparation. However, the optical crosstalk made possible by the subpixelseparation element 20 allows the missing light of the defective subpixel18 to be compensated by the adjacent subpixel 18. Thus, as long as asubpixel 18 of the same color from a group works and the remainingsubpixels 18 of this group are defective, this remaining workingsubpixel 18 could compensate for the malfunctions of the defectivesubpixels and thus ensure a function of the pixel element 12 byredundancy. In an example, an optical crosstalk can also take place overseveral subpixels within a pixel element 12. Other possible arrangementswould be, for example, the assignment of three subpixels 18 each to oneof the basic colors red, green, or blue. Examples are the followinggrouping A/B/C, D/E/F and G/H/K. But also a diagonal assignment isconceivable, whereby an optical crosstalk should be advantageouslypossible.

FIG. 7 shows a sectional view through a section of a display 10. In thelower part of the figure a substrate 14 is shown, which among otherthings should provide a mechanically sufficiently stable supportstructure to accommodate the remaining structural elements. According toone example, this can be a wafer of a silicon IC. The substrate 14 canalso comprise a driver circuit or drive electronics (not shown) andvarious electrical connections. These can, for example, be realized viaconductor structures in the integrated circuit. Furthermore, contactstructures 24 are provided, which can be used to drive a subpixel area26. In the example shown here, this is arranged directly adjacent tocontact structures 24. Via contact structures 24 it is possible tocontrol an emitter chip 26 individually and selectively via the controlelectronics.

An epitaxial layer 26, for example, comprises different layers, whichamong other things allows the functionality of light-emitting diodes.For example, a p-n junction can be implemented by correspondinglydifferently doped layers or can also have one or more quantum wellstructures. Schematically and for simplicity, a region of a p-n junction28 is indicated here by a dotted line. In the epitaxial layer 26, thestructures of the pixel elements 12 and the subpixels 18 are introduced.

In detail, the individual pixel elements 12 can be identified via pixelelement separation layers 16. These each have a length 11, whichcorresponds to a distance between two pixel element separation layers16. Within the pixel elements 12, three sub-pixels 18 can be separatedin the longitudinal direction. These each have a length 12. Subpixelseparation elements 20 are arranged between the individual subpixels 18.

In the example shown here, the pixel element separation layers 16 andthe subpixel separation elements 20 are each designed as a trench orsimilar structure. This means that the pixel element separation layers16 and the subpixel separation element 20 are each incorporated into theepitaxial layer 26 as a trench-like, slit-like or similar structure, forexample by etching processes. An electrically insulating material suchas SiO₂ is then deposited in the trenches. In order to determine theelectrical and optical properties of these trenches, a trench depth d1of the pixel element separation layer 16 is chosen to be larger than atrench depth d2 of the subpixel separation element 20. Thus, it can beachieved that an optical crosstalk between subpixels 18 is possible dueto the smaller depth d2 of the trench of the subpixel separation element20.

In contrast, between two pixel elements 12, both optical crosstalk 30and electrical crosstalk is prevented by the deeper trench d1 of thepixel element separation layer 16. According to one example, a depth d 2of the trench of the subpixel separation element 20 is chosen such thatit passes through an area of a p-n junction 28. This can beadvantageously used to prevent electrical interaction between twoadjacent subpixels 18 or the associated emitter chips 22 and/orelectrical or electromagnetic crosstalk.

In the example above, the pixel element separation layer 16 runs throughthe active layer to the edge of the opposite radiation surface, but doesnot cut through it. This allows the area close to the surface to beformed as a common contact connecting all pixels and sub-pixels with apotential connection. In addition, the pixel element separation layer 16can include a mirror layer so that light generated by the pixel isoptically redirected. In the example of FIG. 7, it is also shown thatthe subpixel separation element 20 passes through the active layer butends shortly after. This prevents electrical crosstalk, but not opticalcrosstalk. Depending on the design and manufacturing parameters, thesubpixel separator element 20 can also reach only to the active layer orslightly into it.

While in this embodiment the pixel element separation layer 16 and thesubpixel separation elements 20 are designed as trenches withsubstantially vertical sidewalls, the invention is not limited to this.It is also possible to choose deliberately other shapes, which also haveadditional functionality such as light collimation or light guidance. Asan example, sloping sidewalls for pixel element separation layer 16 canbe mentioned.

In FIG. 8, an extension of the embodiment in the previous figure isshown. The pixel elements are implemented monolithically in or on a thinfilm substrate. Contacts 26 are arranged on the backside, i.e. the sidefacing away from the main radiation direction. These are locateddirectly below the individual sub-pixels and are formed with aconductive metal, for example a gold or silver alloy. The size of thecontacts essentially corresponds to the area of the individualsubpixels. In this way, a suitable material system can be used toproduce the pixels. In addition, process parameters such as temperature,precursors and others can be adjusted to the pixels to be produced.

Contacts 39 of a backplane or other substrate carrier are arrangedopposite the contacts 26 of the subpixels. The backplane is configuredwith a different material system, e.g. silicon technology. The backplanecontains the control for the individual subpixels as well as their powersupply. Examples of current driver and drive concepts for μ-LEDs aredisclosed in this application. In this version, the backplane includesadditional fuses 42 for each individual subpixel. The fuses are in turnconnected to current driver 40. If a defect occurs in one of thesubpixels during production or a defect occurs during the positioning ofthe pixels on the backplane, the defective subpixels can be separated bymeans of the fuses.

The backplane is positioned with its contacts and then connected to thecontacts of the pixels. Depending on the application, an auxiliarycarrier (not shown here) can be provided to ensure sufficient stabilityfor the pixel elements. For contacting, for example, the two surfacescan be glued together, provided that a conductive connection between thecontacts is guaranteed.

On the other side of the pixel elements, a cover electrode is providedon the one hand, which creates an electrical contact to each subpixel.The cover electrode is led down one or more sides to a contact area. Thecover electrode is transparent and consists for example of ITO. Alongand above the pixel separators 14 additional metallic lines can beprovided on the cover electrode. This reduces the surface resistance ofthe cover electrode and thus improves the current carrying capacity. Theadditional lines at this point do not have a negative effect on lightextraction and shadows do not significantly affect the structure.

A light-shaping structure is arranged next to the cover electrode. Thiscan either be arranged on the cover electrode or extend through thecover electrode and into the semiconductor material of the pixel, insome cases down to active region 28. The light-shaping structurecomprises regions with different refractive indices. Various examples ofsuch a structure are disclosed in this application.

FIG. 9 shows an example. On the one hand, a converter material isincorporated into the light-shaping structure. In particular, the leftside or the left pixel has a light-shaping structure 32 r withconverting properties. This structure converts blue light from eachcontrolled subpixel below the structure 32 r into red light.Accordingly, structure 32 b converts the light emitted by the subpixelsinto green light.

At the same time, the light thus converted is directed through therespective structures 32 r and 32 b in such a way that the convertedlight is emitted directly upwards. In contrast, unconverted light isdeflected in direction so that an exit of unconverted light directlyupwards or parallel to the direction of emission of the converted lightis suppressed. A directional selection can be achieved by photonicstructures presented here.

The directional deflection also extends the path through the convertermaterial, so that the conversion efficiency increases. The unconvertedlight is deflected towards structure 32 b, which collimates light fromblue subpixels.

FIG. 10 shows another viewpoint that is suitable for creating theoptical separation elements. In addition, this embodiment improves therelationship between radiative and non-radiative recombination. Theembodiment makes use of quantum well inter-mixing to create thesubpixels within a pixel. FIG. 10 shows a structure on a non-displayedsubstrate carrier on which semiconductor layer 26 has been grown. Thesubstrate carrier 26 is removed at a later time after transfer to abackplane or an auxiliary carrier. After production of the individualsemiconductor layers with an active region 28 between them, a photomask50 is applied and patterned so that the surface on the semiconductormaterial is exposed, in which the optical and electrical separationelements 16 are manufactured. In a subsequent step, trenches 16 forelectrical and optical separation are etched and filled with aninsulating or dielectric material. Then the photomask 50 isappropriately structured again so that on the one hand the areas on thesurface are exposed in which the electrical separation elements 20 aremanufactured. In addition, a small additional area around the electricaland optical separating elements is freed from photoresist.

In a following step, Zn or another dopant is applied and diffused. Thesesteps can be carried out using, among others, the methods disclosed inthis application. The resulting quantum well intermixing increases theband gap in these areas so that charge carriers see an additional energybarrier. This results in a certain electrical separation between theindividual subpixels. Quantum well intermixing around the optical andelectrical separation elements 16 creates a barrier that keeps chargecarriers away from potential recombination centers and defects createdby the etching process. The photoresist is then removed and the wafer isfurther processed.

FIG. 11 shows a method 100 according to the invention for calibrating apixel element 12. In a first step 110, a subpixel 18 of a pixel element12 is driven as described above and below. This control of the subpixel18 should allow a test of the function of the respective subpixel 18.This can be done, for example, by control signals from an electroniccontrol unit, which in turn can be made possible by contacting eachindividual subpixel 18 separately. In a following step 120, defectinfor-mation of a subpixel 18 is recorded, in other words, informationis generated as to whether the subpixel 18 in question is func-tioningcorrectly.

Such defect information can be, for example, a flag or a certain valuethat contains information about a correct function of subpixel 18. Thisdefect information can be stored according to a following step 130, forexample in a memory unit of a control electronics. This can be used tocompensate defective subpixels by appropriately adapted control signalsof the associated subpixels of the same wavelength and thus to achieve acorrect function of the entire pixel element 12.

In an example, the subpixel separation element 20 may be designed toallow optical crosstalk between subpixels 18 of the same color orwavelength, where the subpixel separation element 20 is designed tooptically separate between subpixels 18 of different color orwavelength.

An extension of pixelated or other emitters in which optical andelectrical crosstalk between pixels of an array is prevented by a pixelstructure with a material bridge is shown in FIG. 12. It illustrates asection of an array A in a cross-section in which two adjacentoptoelectronic pixels P are connected by a material bridge.

Array A features two optoelectronic pixels P in the form of verticalμ-LEDs, which have been manufactured over the entire surface. Each pixelP comprises an n-doped layer 1, a p-doped layer 3 as well as an activezone 5 suitable for light emission. Between the two formed pixels Pmaterial of the layer sequence was removed from the n-doped side andfrom the p-doped side. Only a thin material transition 9 with a maximumthickness dC remains, which comprises the active layer 5 and a thincladding layer 7. The cladding layer can be formed from the samematerial as layers 3 and 5. The material transition is much longer thanit is thick. The thickness dC is selected so that no electromagneticwave can propagate in the material transition. Optical modes are thussuppressed. In other words, the electrical and/or optical conductivityof the material transition 9 in FIG. 12 is effectively reduced in thehorizontal direction.

The two main surfaces of the material transitions 9 and exposed surfaceareas 11 of the pixels P, which are exposed as a result of the removalof the material of the layer sequence, are electrically insulated andpassivated by means of a respective passivation layer 13, which inparticular contains silicon dioxide. The areas of the removed materialof the layer sequence are also filled with a filler material 15.Finally, the two main surfaces of the pixels P are electricallycontacted by means of contact layers 33, whereby these can form endcontacts. Contact layers 33 can have transparent material, for exampleITO, in such a way that the light generated or received by the pixels Pemits through the transparent material.

The active zone 5 comprises one or more quantum wells or otherstructures. Their band gap is tuned to the desired wavelength of theemitted light. The maximum thickness dC is chosen such that allfundamental modes are prevented from propagating along the active zone 5of the material transitions 9 to the next pixel P. The maximum thicknessdC of an active zone 5 of a material transition 9 for this conditiondepends on the refractive index difference between the active zone 5 andthe cladding layers 7 of the material transition 9 corresponding to awaveguide. In general, this means that the material transition should beas thin as possible. On the one hand, this makes crosstalk of opticalmodes more difficult, since the wave cannot propagate in the horizontaldirection. On the other hand, the low maximum thickness dC makes furtherelectrical crosstalk more difficult. The thin cladding layers 7 of theactive zone 5 surrounding the active zone generally show a high surfaceresistance and can only carry little current. A further reduction alsoreduces electrical crosstalk here due to the increasing resistance.

The maximum thickness dC also depends on the refractive index and thethickness of the active zone 5. The maximum thickness dC is greater thanor equal to the thickness of the active zone 5. The maximum thickness dCalso depends on the distance between adjacent pixels P. The greater thedistance, the greater the maximum thickness dC can be. A suggested rangeof the maximum thickness dC is 1 μm and 30 nm.

The layers shown in FIG. 12 have thicknesses that depend on thematerials used, including the doping materials, the doping profile ofthe concentration versus depth, the angles of the sidewalls, the pixelsize, the pixel spacing and the total array size. A lower limit for thetotal thickness is about 100 nm.

Suitable material systems for the pixels P are for exampleIn(Ga,Al)As(Sb,P), SiGe, Zn(Mg,Cd)S(Se,Te), Ga(Al)N, HgCdTe. Suitablematerials for contact layers 33 are metals such as Au, Ag, Ti, Pt, Pd,Cr, Rh, Al, Ni and the like, alone or as alloys with Zn, Ge, Be. Thismaterial can also be used as the filling material 15, which then servesas a bonding material in addition to the filling function. Conductivematerial also has possible reflective and other properties. Transparentconductive oxides such as ZnO or ITO (InSnO) can also be used as contactlayers 33 for bonding and also provide a common contact for either thep-side or the n-side of the array.

Dielectrics such as fluorides, oxides and nitrides of Ti, Ta, Hf, Zr,Nb, Al, Si, Mg can be used as transparent insulators. This material canbe used for passivation layers 13. This material can also be used as thefilling material 15, which then serves as an electrical insulator inaddition to the filling function. Values of the refractive indices ofactive zone 5 and cladding layers 7 depend entirely on the materialsused.

The maximum thickness dC also depends on the refractive index of thedielectric generated by the passivation layer 13 and/or the fillermaterial 15. The smaller the refractive index difference between activezone 5 and dielectric, the greater the maximum thickness dC can be forequal crosstalk.

FIG. 13 shows a second embodiment of a pixel array A in a cross-section.The array A shown here in FIG. 13 differs from the array A shown in FIG.12 in that a light-absorbing material 17 having a relatively small bandgap at least partially fills the areas of the removed material of thelayer sequence. Furthermore, the light-absorbing material 17 adjoinsdirectly at the material transitions 9, since no passivation layers 13are formed at these. Only exposed surface areas 11 of the pixels P areelectrically insulated and passivated by means of a respectivepassivation layer 13. Their material can contain silicon dioxide, forexample, so that no electrical short circuit occurs between material 3and 17.

In FIG. 13—not shown there—alternatively only one—in FIG. 13 upper orlower—side of the material transition 9 between the two pixels P isfilled by the light absorbing material 17. On the other side, forexample, a filling material 15 is formed at the material transition 9,leaving the passivation layer 13 between them. By using thelight-absorbing material 17, additional suppression of optical crosstalkis provided. The light-absorbing material 17 between the pixels Preduces wave guiding by absorbing the light that leaves the active zone5 in the area of the material transitions 9. There is an attenuation ofthe waveguide along the material transitions 9.

Suitable light-absorbing materials 17 are metals, alloys, dielectrics orsemiconductors with a smaller band gap than the band gap of the materialtransition 9, which initially acts as a waveguide. This means that theenergy of the light is also greater, so that it is absorbed by thematerial 17. For example, floating eye can be used, which absorbs 50% ofred wavelengths. The light-absorbing material 17 is grown at thematerial transitions 9, for example by CVD (chemical vapour deposition)or PVD (physical vapour deposition) by creating epitaxial layers. Thelight absorbing material 17 was applied or grown on the cladding layers7.

FIG. 14A shows a third embodiment of a pixel array A in a cross-section.At the locations of the material removed from the n-doped and/or fromthe p-doped side of the layer sequence of the pixel array, a material 19is formed with a refractive index which is larger compared to theremoved material, in particular to the doped material or a fillermaterial 15, but which should not be greater than the refractive indexof the cladding layers 7 or the active zone 5. This also attenuates thewaveguide in the material transition 9. The layer sequence on thesubstrate 35 is finally covered by a protective top layer 37.

The material 19 with an increased refractive index is grown epitaxiallyat the material transitions 9, for example by means of chemical orphysical vapor deposition. The application or growth takes place afterthe removal of the original n-doped and/or p-doped layer materialbetween two pixels P each and after passivation of exposed surface areas11, in particular side areas, of the pixels P by applying passivationlayers 13.

The material 19 with increased refractive index was applied or grown onthe cladding layers 7. No passivation layers 13 are formed at thematerial transitions 9. This is the area below the material transition9. For example, GaAs as material 19 with increased refractive index canbe grown on an active zone 5 of a material transition 9, which containsAlGaAs. Alternatively, the material 19 with increased refractive indexis formed by diffusing or implanting a refractive index increasingmaterial 21 into a filler material 15 up to or into the cladding layers7. This is represented in FIG. 14A by the area above the materialtransition 9. Increased refractive index material 19 may be formed abovethe material transition 9 and/or below the material transition 9 in FIG.14A. An area free of material 19 with a higher refractive index can befilled with a filler material 15.

FIG. 14B shows a simulation of the propagation of light in the area ofthe material transition of the third embodiment of a pixel arrayaccording to the proposed principle. It shows the cross section of amaterial transition 9 where only an upper side has been etched andfilled with a material 19 with an increased refractive index. Thematerial 19 with an increased refractive index has a refractive indexequivalent to the quantum well material 5, i.e. the active zone 5 andthe material 19 with increased refractive index are shown in dark greyin the diagram. The cladding layer 7 or non-etched semiconductormaterial of an n-doped layer 1 and a filler material 15 are shown inwhite.

The 0.1 μm thick layer is the active zone 5 or the area of the quantumwell material. The 0.05 μm thick layer is still “residual cladding” or aremaining cladding layer 7. The fpm thick layer is the material 19 withthe increased refractive index.

In the area of the material transition 9 between two pixels P, an activezone 5 with a refractive index of 3.5 and a layer thickness of 0.1 μm isarranged on a lower, unetched n-doped layer 1 having a refractive indexof 3. On this first inner layer, a cladding layer 7 with a refractiveindex of 3 is formed as a second inner layer of the material transition9 with a layer thickness of 0.05 μm. A relatively thick third innerlayer of a material 19 with an increased refractive index of 3.5 and alayer thickness of 1 μm is formed thereon. The third inner layer iscovered by a layer comprising a filler material 15 with a refractiveindex of, for example, about 3.

For a simulation on this layer structure, a vacuum light wavelength of0.63 μm was assumed. The generated light can be TM- and/or TE-polarized. One speaks of TM-polarized light when the direction of themagnetic field is perpendicular to the plane (“plane of incidence”)defined by the vector of incidence and the surface normal(TM=transversely magnetic), and of TE-polarized light when the electricfield is perpendicular to the plane of incidence (TE=transverselyelectric). For the simulation, FIG. 14B with the x-axis represents thevalue of a spatial extension x in μm. The y-axis shows the value of ay-component of an electric field strength E. FIG. 14B shows how afundamental mode TE0 emerges from the active zone 5 and is stopped bythe other optical barriers present between two pixels P above and/orbelow the material transition 9 acting as a waveguide. The opticalbarriers here are the interfaces between the layers of differentrefractive indices according to the layered structure of FIG. 14Adescribed above. The fundamental mode TE0 enters the thick third innerlayer of material 19 with increased refractive index and does not reachthe adjacent pixel P.

In practice, a material with a higher refractive index is often also amore absorbent material, especially due to a smaller band gap.

FIG. 15 shows a fourth embodiment of a pixel array A in a cross-section.Identical reference signs to the other FIGS. 141 to 140A indicateidentical features in FIG. 15. In contrast to a design according to FIG.12, here between two filler layers 15 and two passivation layers 13,additional material 23, 24 is introduced into the active zone 5 of amaterial transition 9, which effectively reduces electrical and/oroptical conductivities of the material transition 9 acting as waveguide.The additional material is, on the one hand, a material 23, whichincreases light absorption in the active zone 5 of the materialtransition 9. Absorption in the active zone 5 between pixels P isincreased by reducing the bandgap of the material of the active zone 5.For this purpose, bandgap-reducing elements are implanted or diffusedinto the active zone 5 of the material transition 9. In particular,dopants are diffused or implanted into the central region of the activezone 5 between pixels P. The reduction of the band gap is achieved by aso-called band gap renormalization. The greater the amount of material23 introduced along a material transition 9, the greater the absorptionof light in the active zone 5.

Alternatively or cumulatively, the additional material is, on the otherhand, a material 24, which increases an electrical resistance in theactive zone 5 of the material transition 9. For this purpose, elements,which increase the electrical resistance, are implanted or diffused intothe active zone 5 of the material transition 9. This further increase inelectrical resistance serves to reduce further electrical crosstalk fromone pixel P to the adjacent pixel P. For example, to increase theelectrical resistance Fe can be implanted in an active zone 5 of amaterial transition 9 with InGaAsP. The greater the amount of material24 introduced along a material transition 9, the greater the increase inelectrical resistance of the active zone 5 of the material transition 9between two pixels P.

Materials 23, 24 are both diffused or implanted into the active zone 5of a respective material transition 9 before the application ofpassivation layers 13.

FIG. 16A shows a further example of a pixel array A in a cross-section,in which, in contrast to a structure in FIG. 12, an optical structure 25is incorporated in the area of the material transition. The structure 25is inserted between two filler layers 15 and two passivation layers 13along the active zone 5 of a material transition 9. This reduces anoptical conductivity of the material transition 9 acting as waveguidebetween two pixels P. A waveguide is reduced. Optical structures 25 canbe a photonic crystal and a Bragg mirror or another dielectricstructure. The structure 25 forms periodic structures of the refractiveindex along the material transition 9 above, below or on both sides ofthe active zone 5, which leads to an optical band gap and prevents thepropagation of photons along the material transition.

The periodicity of the optical structures depends on the lightwavelengths, the size of the optical structures, the length of thestructured material transition 9 and the refractive indices of thematerials used. FIG. 16A shows only one optical structure 25 on a lowerside of the material transition 9, which acts as a waveguide. Thisoptical structure 25 can also be formed on the upper side of the waveguiding material transition 9. The optical structure 25 shown in FIG.16A is a Bragg mirror. After forming the optical structure 25,passivation layers 13 are applied.

An extension of the example in FIG. 16A is shown in FIG. 16B. Aconverter material 41 or 42 is applied to the surface. The convertermaterial 41 and 42 extends to approximately the middle between twoμ-LEDs. As the walls of the μ-LED are self-reflecting, the lightgenerated in the active layer of a μ-LED is directed by the μ-LEDstowards the converter material. Light that enters the converter materialfrom the μ-LED is converted there. Crosstalk is prevented by an optionalreflective layer between the converter materials.

On the surface of the converter materials, photonic structures 34 and 37are deposited on each pixel to direct the light. In an alternativeembodiment, the photonic structure extends into the converter materialor even into the semiconductor material.

FIG. 17 shows a sixth embodiment of pixel array A in a cross-section inaccordance with the invention. In contrast to an embodiment according toFIG. 13, in two filler layers 15, along the active zone 5 of a materialtransition 9, two additional electrical contacts 27 are introduced atboth main surfaces of the material transition 9 acting as waveguide,which effectively reduces electrical and/or optical conductivities ofthe material transition 9 acting as waveguide between two pixels P.These opposite electrical contacts 27 apply an electrical bias to bothmain surfaces of a respective material transition 9 between two pixelsP.

By means of the applied electrical bias voltage (Bias), a staticelectrical field is generated, by means of which the optical propertiesof the material transition 9, which initially acts as a waveguide, arechanged in such a way that a waveguide along the material transition 9is effectively reduced.

As a result of applying the electrical bias to the material transition 9between the pixels P, which initially acts as a waveguide, an absorptionof light in the waveguide is increased by means of the so-called“quantum confined Stark” effect (QCSE; limited Stark effect), as is usedin an electro-absorption modulator, for example. In anelectro-absorption modulator, the fundamental absorption of asemiconductor is effectively increased by applying an electric field.Accordingly, optical crosstalk between pixels P is reduced. Suitableelectrical contacts 27 are conventional Schottky contacts ormetal-insulator contacts. Furthermore, everything that is conventionallyused for band bending without current flow is suitable.

After the two opposing electrical contacts 27 have been formed,passivation layers 13 are applied to the two opposing electricalcontacts 27, in particular to their surfaces where filler material 15 isformed and which are adjacent to the pixels P. Identical reference signsto the other FIGS. 138 to 142A are shown in FIG. 17, which showsidentical characteristics.

FIG. 18 shows a seventh embodiment of a pixel array A in across-section. In contrast to the embodiment in FIG. 17, an electricfield is generated here inherently, i.e. by selecting a suitablematerial system. For this purpose, at least one layer of n-dopedmaterial 29 and/or p-doped material 31 is arranged on at least one ofthe two main surfaces of a material transition 9 in such a way that anelectric field is generated by it, which is thus incorporated into thematerial transition 9 without further means. If only one layer of dopedmaterial is formed on one of the two main surfaces of the materialtransition 9 and the layer on the other main surface of the materialtransition 9 is undoped, a so-called depletion field is provided whichis sufficient as an electric field to increase light absorption in thematerial transition 9. Alternatively, the electric field for increasinglight absorption in the material transition 9 is generated by forming alayer of n-doped material 29 on one main surface of the materialtransition 9 and a layer of p-doped material 31 on the opposite mainsurface of the material transition 9.

The material used to provide the electric field, in particular then-doped material 29, the p-doped material 31 and possibly the undopedmaterial are grown epitaxially by means of CVD (chemical vapordeposition) or PVD (physical vapor deposition) in such a way that abuilt-in bias is provided between adjacent pixels P on the thinwaveguide. For n- and μ-doping, InGaAlP can be doped with Si and Zn.

By means of the doped material 29 and/or 31, a bias is provided whichhas the same effect as the embodiment as shown in FIG. 17. Furthermore,the material providing the electric field is directly applied to thematerial transitions 9, as no passivation layers 13 are required atthese. Only exposed surface areas 11 of the pixels P are electricallyinsulated and passivated by a respective passivation layer 13. Theirmaterial may contain silicon dioxide, for example. The pixels P areelectrically connected via electrical contact layers 33.

FIG. 19 shows an eighth embodiment of a pixel array A in across-section. In this example, the active zone 5 was etched in acontrolled manner. In other words, damage to the active zone 5 or theoccurrence of defects in the active zone 5 in the area of the materialtransition is allowed in a controlled manner. According to FIG. 19, thematerial transition 9 is completely interrupted in its center to the twopixels P, between which the material transition 9 is formed. At thetransitions to the two pixels P, the material transition 9 is formedwith a maximum thickness dC.

FIG. 20 shows a ninth embodiment of a pixel array A. On the left side,two different embodiments of the suppression of crosstalk between twoadjacent pixels P are shown in cross section. The upper variant V 1shows the first embodiment according to FIG. 12, the lower variant V 2shows the fourth embodiment according to FIG. 16A. On the right side, atop view of four adjacent pixels P is shown.

Four adjacent pixels P are assigned to each pixel P, whereby here alongan x-direction material transitions 9 are formed according to the secondvariant V 2. Along a y-direction the material transitions 9 are formedaccording to the first variant Vl. In principle, each materialtransition 9 to the other material transitions 9 can be designeddifferently, in accordance with the embodiments described in thisapplication. In principle, material transitions 9 can be designed in thesame way along a respective spatial direction. The material transitions9 can be designed according to the desired patterns. The materialtransitions 9 along a respective spatial direction can alternate indesign.

In this way, an array A according to this application includes allpossible embodiments or variants as well as combinations of embodimentsof material transitions 9. The plan view in FIG. 20 shows that allvariants V can be combined depending on the direction, for example. Thisalso applies to all possible shapes of pixels P, which can be round orsquare, especially here rectangular.

FIG. 21 shows an example of a method of manufacturing a pixel array Aaccording to the invention. The method of manufacturing an array A ofoptoelectronic pixels P comprises the following steps. In a first stepSi, a whole-surface layer sequence of an n-doped layer 1 and a p-dopedlayer 3 is generated along the array A, between which an active zone 5is formed. Various techniques are explained and disclosed in thisapplication.

In a second step S2, material of the layer sequence is removed betweenpixels P to be formed, in particular by etching, from the n-doped sideand from the p-doped side. This is done in such a way that at least theactive zone remains as a material transition. Likewise, thin claddinglayers 7 can remain in the material transition 9 above or below or onboth sides of the active zone 5. The thick dC is thus significantlyreduced and optical modes cannot propagate laterally between the pixels.The higher resistance also reduces electrical crosstalk. Over-all, theelectrical and/or optical conductivity of the material transitions 9 isreduced.

The thickness dC is sufficiently thin, which is required ac-cording tothe specifications for array A or for a desired device in terms ofbrightness or responsivity. The thickness in the area of the materialtransition depends, among other things, on the material system and thewavelength of the emitted light.

In one aspect, etching is performed from both sides up to or into thethin mantle layers 7 on each side of the active zone 5 or up to theactive zone 5, in such a way that all fundamental modes are preventedfrom propagating along the active zone 5 to the next pixel P. Themaximum thickness dc of an active zone 5 of a material transition 9 forthis condition depends on the refractive index difference between theactive zone 5 and the cladding layers 7 of the material transition 9acting as a waveguide.

Reducing the maximum thickness dC results in a reduction of opticalcrosstalk because more light is emitted from the waveguide. A reductionof the thickness dC also means a reduction of electrical crosstalk. Thethin undoped cladding layers 7 of the active zone 5, which remainbetween individual pixels P, can hardly carry any current. Thistherefore reduces electrical crosstalk.

With further steps S3 to S5, after etching, the individual pixels P andthe waveguide can be covered with other materials necessary for furthersuppression of optical and/or electrical crosstalk outside thewaveguide. In step S3, the exposed main surfaces of the materialtransitions 9 and exposed surface areas 11 of the pixels P areelectrically insulated and passivated by means of a respectivepassivation layer 13, in particular comprising silicon dioxide. Theelectrical insulation and passivation of the exposed main surfaces ofthe material transitions 9 can be omitted, depending on which measure isused in the fourth step S4 to reduce crosstalk.

In a fourth step S4, from the n-doped side and/or from the p-doped side,the removed material is at least partially replaced, e.g. by a fillermaterial 15. In step S5, contact layers 33 are applied to the mainsurfaces of the Pixel P and thus the structure is electricallycontacted. According to one design, steps S1 to S5 are first performedfor one main surface of the array and then, after a substrate change,for the other main surface of the array.

To reduce further optical and/or electrical crosstalk, further measurescan be taken in the fourth step S4 cumulatively to form the materialtransitions 9 with the maximum thickness dC. Some of these are listedhere as examples, others are described above for the various embodiment.For example, from the n-doped side and/or the p-doped side, areas of theremoved material can be filled with light-absorbing material 17 and/orwith more strongly refractive material or material 19 with an increasedrefractive index instead of filling material 15. No passivation layer 13is formed here at the material transitions 9.

Furthermore, in the fourth step S4, the light absorption and/or theelectrical resistance of the active zone 5 can be increasedalternatively or cumulatively. A passivation layer 13 should also beapplied to the material transitions 9.

The application of these concepts allows the manufacturing of arrays Aof optoelectronic pixels P, in particular micropixel emitter anddetector arrays without etching through the active zone 5, withoutoptical and electrical crosstalk and without performance and reliabilityproblems compared to solutions with etched active zones.

FIG. 54 shows a modular architecture of subunits of μ-LEDs. These showdifferent horizontal μ-LEDs, which are combined in so-called basemodules for the provision of μ-LED modules. The base module comprises alayer stack, which has a first layer 3 formed on a carrier orreplacement carrier 1, on which an active layer 7 and on which a secondlayer 5 is formed. A first contact 9 is applied to a surface area of thesecond layer 5 facing away from the carrier 1, and a second contact 11is connected to a surface area of the first layer 3 facing away from thecarrier 1. The second contact 11 is electrically insulated from theactive layer 7 and the second layer 5 by means of a dielectric 10 and isformed to and on the surface region of the second layer 5 facing awayfrom the carrier 1.

When manufacturing the base module, a surface area of the first layer 3facing away from the carrier 1 must be exposed after the generation ofthe layer stack. This means that material of the second layer 5, theactive layer 7 and partly of the first layer 3 is removed at an edgearea of the layer stack.

This can be carried out, for example, by means of flank structuring ofthe at least one stack of layers, in particular from the side of thesecond layer 5, a trench being created surrounding the at least onestack of layers, in particular in a flank structuring area 13. A layerstack can also be described as a mesa structure. The trench is alsoreferred to as a mesa trench. The flanks of a stack of layers are calledmesa flanks accordingly. This structuring is carried out usingappropriate masks.

In the case of edge structuring, etched areas can be coated with aninsulating layer or a dielectric, especially by means of inductivelycoupled plasma ICP or reactive ion etching RIE, using chemical vapordeposition. The dielectric used is SiO or ZnO. The second contact 11 canhave ITO (indium tin oxide) and is produced by sputtering or physicalvapor deposition.

A plurality of base modules can be generated as a matrix along an X-Yplane along at least one row and along at least one column on a carrier1. For this purpose, in addition to the flat one, a further, deep flankstructuring through carrier 1 and the first layer 3 is implemented onthe right edge area. Area 15 corresponds to the deep flank structuring.

In this way, one module from a matrix of a plurality of base modules canbe removed from a carrier 1. The deep edge structuring can be carriedout by etching, in particular dry chemical etching or plasma etching.

FIG. 55 shows an example of the embodiment of a base module B as shownin FIG. 54, arranged upside down on another carrier or end carrier 2.The further carrier or end carrier 2 can be transparent to the lightemitted by the optoelectronic component. In addition, the material ofcarrier 1 has been removed.

This can be done, for example, by grinding away or by so-called laserlift-off (LLO). The base module B is thus arranged as a flip chip on thefurther carrier or end carrier 2 and contacted there.

FIG. 56 shows the embodiment according to FIG. 55 with a further basemodule B with edge area 15 ′ without carrier 1. Both base modules B areoriented opposite to each other, whereby identical contacts, namelyfirst contacts 9, are arranged adjacent to each other. Both base modulesB may originally have been formed on carrier 1 in two adjacent rows of amatrix. After removing carrier 1, base modules B are arranged upsidedown on another carrier or end carrier 2. The two adjacent base modulesB, oriented opposite to each other, have been created here as a commonlayer stack. In this case, the dashed line 17′ in FIG. 56 would be asurface area of the second layer 5 in the middle between the two basemodules. However, to prevent crosstalk, layer 5 in the middle has beenremoved by structuring. After such structuring, which also cuts throughthe active layer, the solid line 17 shows a surface area of the firstlayer 3.

FIG. 57 shows the embodiment according to FIG. 56 with separatecontacting of the contacts. First contacts 9 and second contacts 11 areelectrically isolated and connected to corresponding contacts on the endcarrier 2. A first contact 19 is electrically connected to the firstcontact 9 of each module and a second contact 21 is electricallyconnected to a second contact 11. Contacts 21 and 19 have been made inprevious steps in end carriage 2. The base modules are then placed onthe end carrier 2, thus creating an electrical connection.

As in the previous version, the middle area is partially removed byadditional structuring. Alternatively, it can also be left in place.

FIG. 58 shows the embodiment according to FIG. 56 with common contactingof the first contacts. Second contacts 11 are electrically isolated andconnected to contacts of end carrier 2. A first contact 19 applied to asurface of the end carrier 2 is electrically connected to two firstcontacts 9. Second contacts 21 are electrically connected separately tosecond contacts 11.

As in the previous version, the middle area is partially removed byadditional structuring. Alternatively, it can also be left in place.

In FIGS. 56 to 58, a first layer 3, a transition layer 7 and a secondlayer 5 can be completely removed as a result of a deep flank structurebetween the two base modules B. The two base modules B can be contactedto the further carrier or end carrier 2 using flip-chip technology.

FIG. 59 above shows another example of the embodiment of a proposed basemodule B of a single μ-LED to provide a μ-LED module with two rows andtwo columns of base modules B as shown below. The base module B shownabove can be provided here on a carrier 1 but also without a carrier. Inthis top view, a first contact 9 and a second contact 11 are visible,and in addition, the first layer 3, the transition layer 7 and thesecond layer 5 are shown.

As shown in FIG. 59 below, four base modules B have been groupedtogether to form a μ-LED module. Already on carrier 1, this matrix withtwo rows and two columns in an X-Y plane may have been selected. Whenproducing adjacent rows on carrier 1, the base modules B of a row can beoriented in the same way. Here, the lower row has base modules B, whichare arranged opposite to the upper base modules B. The μ-LED moduleshown in FIG. 59 below can still be arranged on the not shown carrier 1after a flat edge structuring. It is grouped into the rectangular LEDmodule by selecting a release area. This is extracted by means of a deepedge structuring along a rectangle surrounding the μ-LED module. Theresulting 2×2 (two rows by two columns) μ-LED module comprises a widthof approximately 20 micrometers and a length of approximately 30micrometers.

FIGS. 60A to 60D show four cross-sections of two oppositely orientedbase modules B, which are arranged upside down, i.e. as flip chips onanother carrier or end carrier 2. A base module B can have a width ofapproximately 10 micrometers and a length of 15 micrometers. Dependingon the masking during mesa etching, especially to provide a shallow edgestructuring, precursors of μ-LED modules can be created, which cansubsequently be removed from a carrier, especially carrier 1, to or as alight emitting diode module, especially by means of a deep edgestructuring. Reference symbol 10 designates a dielectric.

According to FIG. 60A, two oppositely oriented individual base modules Bare arranged adjacent to each other. Their first contacts 9 are incontact with each other, but do not touch each other. The cross sectionaccording to FIG. 60A shows that a flat flank structure was brought outfrom the side of the second layer 5. This creates a shallow trench thatruns around a respective base module B or a respective layer stack. Adeep flank structuring was led out from the side of the first layer 3 sothat the individual base modules are separated. In this way, severalbase modules still connected to each other are first placed on the endcarrier 2 and then separated from the side 3 by means of the flankstructuring. The original carrier 1 was removed.

According to FIG. 60B, two oppositely oriented individual base modules Bare also arranged adjacent to each other. Their first contacts 9 are incontact with each other, but do not touch each other. The cross-sectionaccording to FIG. 60B shows that a shallow flank structuring of thelayer stacks was carried out from the side of the second layer 5. Incontrast to FIG. 60A, a deep flank structuring of the layer stacks wascarried out from the side of the second layer 5, i.e. from the same sideas the shallow flank structuring. The original carrier 1 was removed.

FIG. 60C shows an intermediate step. After that, two oppositely orientedbase modules B are arranged, which are created together as one piece.Their first contacts 9 are adjacent to each other. A common layer stackof two adjacent base modules oriented in opposite directions to oneanother is produced, with a first layer 3, a transition layer 7 and asecond layer 5 each being produced as a unit along the end carrier 2.The cross section according to FIG. 60C shows that a shallow flankstructuring of the layer stack was performed from the side of the secondlayer 5, with only the edge areas of the two second contacts 11 having ashallow flank structuring. The area between the first two contacts 9 isnot flank structured, i.e. the second layer 5 there remains unprocessed.After contacting, a deep edge structuring of the layer stack is carriedout here as shown in FIG. 60A from the side of the first layer 3 and themodules are separated (not shown). The original carrier 1 has beenremoved.

According to FIG. 60D, two oppositely oriented base modules B are alsoarranged, which were created as one piece. Their first contacts 9 areadjacent to each other. A common layer stack of two adjacent basemodules oriented in opposite directions to each other has been produced,whereby a first layer 3 has been produced as one unit along the endcarrier 2. The cross-section shown in FIG. 60D shows that a shallowflank pattern has been created on the stack of layers from the side ofthe second layer 5, creating a shallow trench around each base module B.In particular, the area between the two first contacts 9 is flankstructured, i.e. the second layer 5 there and the transition layer 7 aswell as part of the first layer 3 have been removed there as well as inthe edge area of the second contacts 11. A deep flank structuring of thestack of layers was carried out here, as in FIG. 60B, from the side ofthe second layer 5. Only a small ridge remains in the figure, but thiscan still be separated if necessary.

FIG. 61 shows a further illustration of an embodiment of a proposed basemodule B to provide a μ-LED module with two rows and three columns (2×3)of base modules B, as shown below the base module B shown above can beprovided here on a carrier 1, but also without a carrier. In this planview, a first contact 9 and a second contact 11 are shown, as well asthe first layer 3, the transition layer 7 and the second layer 5 arevisible.

According to FIG. 61 below, six base modules B are grouped together toform a μ-LED module. This matrix with two rows and three columns in anX-Y plane is already selected on carrier 1. In addition, when producingadjacent rows on carrier 1, the base modules B of one row are orientedin the same way. The lower row here has base modules B, which arearranged opposite to the upper base modules B. The μ-LED module shown inFIG. 61 below can still be arranged on carrier 1 after a flat edgestructuring. A grouping into the rectangular LED module shown belowtakes place by selecting a release area. This can be detached by meansof a deep edge structuring along a rectangle enclosing the μ-LED module.The generated 2×3 (two rows by three columns in an X-Y plane) μ-LEDmodule has a width of approximately 30 micrometers and a length ofapproximately 30 micrometers. With this method, any combination of amatrix of base modules can be extracted and produced as a μ-LED module.

FIGS. 62A to 62D show four cross sections of two oppositely orientedbase modules B of a μ-LED module as shown in the lower illustration inFIG. 61.

FIG. 62C shows, in contrast to FIG. 60C, that the first contacts 9 areelectrically connected and contacted by means of a common first contact19 created on the end carrier 2. The second contacts 11 are individuallyelectrically connected to second contacts 21 on the end carrier.

FIG. 62D shows, in contrast to FIG. 60D, that first contacts 9 areindividually connected to first contacts 19 and second contacts 11 areindividually connected to second contacts 21 of the end carrier 2.

FIG. 63 shows a top view of a matrix of a carrier (wafer or carrier 1)with groupings in an X-Y plane, which has base modules B. The basemodules B are all originally generated on a carrier, in particularcarrier 1, in the same orientation. There was no rotation or rotation ofbase modules B. A generated μ-LED module only comprises one base moduleB in a Y-direction and is therefore single-line. Any number of basemodules can be provided in an X direction. In FIG. 63 base modules Bhave been grouped into four μ-LED arrays or μ-LED modules M.

FIG. 64 shows a top view of a matrix of a carrier (wafer or carrier 1)with other groupings, which comprises base modules B. Here, the basemodules B of two adjacent rows are oriented opposite to each other byrotating the base modules B of one of these rows. The dotted linesrepresent the rectangles of the μ-LED modules M still to be separated.FIG. 64 shows μ-LED modules M with one or two rows along a Y-direction,whereby the number of columns in the X-direction can be arbitrary.

FIG. 65 shows another top view of a further matrix of a carrier, inparticular a carrier 1 or wafer, with a further grouping, whichcomprises base modules B. This grouping creates a rectangular μ-LEDmodule M in an X-Y plane, which comprises three rows and five columns.The μ-LED module M thus has 15 base modules B, which are evenlydistributed in the rectangle. The base modules B are equally spacedalong one row. The rows are also equally spaced. All base modules B havethe same orientation.

FIG. 66 shows a further top view of a further matrix of a carrier, inparticular a carrier 1 or wafer, with a further grouping, whichcomprises base modules B. This grouping creates a rectangular μ-LEDmodule M in an X-Y plane, which has four rows and three columns. Theμ-LED module M thus comprises 12 base modules B, which are evenlydistributed in the rectangle. The base modules B are equally spacedalong one row. The base modules B comprise two pairs of lines, wherebyin one pair of lines the base modules B of both lines are orientedopposite to each other and are equally spaced apart. The distancesbetween the pairs of lines can be different from the distances betweenthe lines in a pair of lines. In this way, a chip cluster of μ-LEDs canbe formed on a carrier 1 or wafer. The result is a modular μ-LEDarchitecture.

The manufactured μ-LED modules M can be electrically contacted by meansof flip-chip technology and integrated into μ-LED displays, for example.Base modules B can be electrically connected in series or in parallel.

FIG. 67A shows an embodiment in which the μ-LED module was structuredeither after the intermediate transfer step or before on the lightemission side. Several periodically arranged holes were etched into thesemiconductor layer facing the light emission side, which can bedescribed as so-called negative pillars or columns. This result in aperiodic variation of the refractive index, since the surroundingsemiconductor material comprises a higher refractive index than theholes filled with air. In this embodiment, the depth of the periodicstructure reaches approximately to the active region, but is at least inthe order of one wavelength of the light to be emitted. In thisembodiment, the holes in the semiconductor material are not filled.However, it can be useful to fill them with a material with a differentrefractive index in order to achieve the desired optical properties onthe one hand and to achieve a planar surface on the other.

The μ-LED modules can be transferred to a backplane after deep edgestructuring as well as after a complete etching. The deined size of theμ-LEDs from the combined base modules isparticularly suitable for this,as it defines the distances in a fixed manner. In addition, a class ofstamps can possibly be used to transfer modules of different sizes. FIG.67B illustrates an example of such a transfer process with a stamp, asdescribed in more detail in this application. Stamp 20 has severalcushions 21 and 22, spaced at fixed intervals, each of which can becharged with a surface tension or surface charge, as described in thisapplication. The distances between the cushions correspond to the sizeof the individual base modules of each base module.

If a base module or μ-LED module is to be removed from the composite andtransferred, the stamp generates a potential on its side facing themodule so that it adheres to the cushion. The adhesive force isdetermined by the charge or voltage of a cushion. In this respect,larger modules can also be transferred, provided that the electrostaticforce generated by the cushions is sufficient.

FIG. 68 shows an example of a proposed method for the manufacture oflight emitting diode modules. In a first step S1, at least one layerstack providing the base module is created. The stack comprises a firstlayer formed on a carrier 1, on which an active layer and a second layerare applied. The active layer can comprise a quantum well or similar.

In a second step S2, a surface area of the first layer facing away fromsubstrate 1 is exposed. Finally, in a third step, a first contact isapplied to a surface area of the second layer facing away from carrier1. In addition, a second contact is created on the surface area of thefirst layer facing away from carrier 1 and exposed. The second contactis electrically insulated from the transition layer and the second layerby means of a dielectric and runs on the surface area of the secondlayer facing away from carrier 1.

In this way, any number of base modules can be generated as a matrix ona wafer or carrier 1, whereby the base modules can be grouped into μ-LEDmodules and then separated. LED modules preferably have a rectangular orsquare shape in an X-Y plane of the matrix. In this plane, base modulescan be arranged regularly in the rows and columns with equal spacing.The base modules are preferably generated and arranged evenlydistributed along the matrix over a wafer, carrier or replacementcarrier 1.

The manufacturing process shown here is greatly simplified. In fact, alarge number of the techniques described here can also be used. Forexample, each base module can have a current constriction by doping thechange in band structure accordingly. Since the base modules areseparated if necessary, it is also advisable to change the band gap ofthe material system and the active layer at the possible predeterminedbreaking points by quantum well intermixing or other measures. Thisreduces non-radiative recombination at possible edge defects, since thecharge carriers are repelled by the changed potential of the bandstructure. The manufactured μ-LED modules can still be structured in thesurface to improve the radiation characteristics. This makes it possibleto apply a photonic crystal or a converter layer to larger modules ormodules of different colors. Each μ-LED module can also be equipped withits own control unit, which has already been implemented in the endcarrier 2.

Another aspect deals with the question whether and to what extent suchsub-units with sensor can be provided. As already mentioned, themanufactured and grouped modules are transferred to a target matrix,which comprises for example a backplane or similar.

FIG. 69 shows the steps S1 to S5 of a proposed process for theproduction of a display with such sensors, which will be manufacturedusing the modules presented here.

The method is used to produce a μ-display with a full-surface targetmatrix of components, in particular μ-LEDs 5, arranged in rows andcolumns next to each other on a first carrier 3 or end carrier. Theμ-LEDs in turn are part of modules.

In a first step S1, a number of μ-LEDs 5 are formed on a carrier or areplacement carrier 17 in a starting matrix 7. The spacing and size ofthe μ-LEDs 5 in the start matrix 7 are in a fixed, in particularinteger, ratio to the spacing and size of the free spaces of the latertarget matrix 1 on the first carrier or end carrier 3. The μ-LEDs areformed by the methods described in this application. In particular, thewafer is prepared for deep mesa etching in order to obtain a modulestructure. The individual μ-LEDs later form the subpixels or also pixelson the target matrix. In this respect, the start matrix 7 can becongruent with at least part of the target matrix 1. In this way, groupsof components 5 can be transferred for this part from the replacementcarrier 17 to the final carrier 3. Correspondingly, the replacementcarrier with the μ-LEDS formed on it can be at least partially congruentwith the end carrier in terms of size and spacing.

In a second step S2, the μ-LEDs 5 are grouped to a number of modules 9on the replacement carrier 17, especially by means of deep mesa etching.

In a subsequent step S3, the modules 9 structured in this way are liftedoff the replacement carrier 17, in particular by means of laser lift-offor a mechanical or chemical process, and then transferred as modules tothe final carrier 3 and thus to the target matrix 1. Contact areas ofthe modules contacting the μ-LEDs 5 are configured in such a way thatthey correspond to contact areas of the target matrix after thetransfer. In other words, for at least a partial area of the finalcarrier 3 and thus the target matrix 1, the modules and the μ-LEDs arearranged with their contact areas on the replacement carrier 17 in rowsand columns next to each other in such a way that the distances betweenthe μ-LEDs 5 on the replacement carrier 17 are equal to the distancesbetween the μ-LEDs 5 on the target matrix 1 of the final carrier 3.

In the fourth step S4, the modules 9 are positioned and electricallyconnected to the primary end carrier 3 in the target matrix 1 in such away that a number of unoccupied positions 11 remain in this matrix. Forthis purpose, the modules themselves may be unevenly designed, so that,for example, one module is missing. Alternatively, the modules can alsobe transferred to the target matrix in such a way that some positions,for example rows or columns, remain unoccupied.

In a fifth step S5, at least one sensor element 13 is positioned andelectrically connected at least partially at each of the unoccupiedpositions 11.

FIG. 70A shows a diagram to illustrate the different aspects anddifferences between μ-LED, module and the replacement carrier.Replacement carrier 17 comprises a sapphire substrate on which varioussemiconductor layers, including at least one active layer, have beendeposited in several steps disclosed in this application. A startingmatrix 7 of μ-LEDs is created on the replacement carrier 17 by means ofshallow etching. The μ-LEDs 5 are still interconnected and have onlyelectrically mutually insulating areas created by means of shallowetching, so that they can be individually addressed. Such methods aredisclosed in this application. In one aspect, vertical μ-LEDs are formedin which a first contact faces the substrate and a second contact facesaway from the substrate. In addition to this embodiment, μ-LEDs can alsobe produced which are designed as flip-chips with their contacts next toeach other on the same side. In the present example, a μ-LED 5 isdesigned as a flip chip, with the two contacts facing away from thesubstrate and electrically insulated from each other. The μ-LED 5 formsa cuboid element. The μ-LED 5 represents a basic element and comprises,for example, a width of approximately 10 μm and a length ofapproximately 15 μm. A component 5 is shown as a base unit on the leftside of FIG. 70A.

By means of an additional, this time deep mesa etching—this correspondsto the second step S2 of FIG. 69—the μ-LED 5 are grouped to modules 9.In the middle of FIG. 70A, a start matrix 7 of twelve components 5 iscreated on the replacement carrier 17 by means of a shallow etching,whereby the μ-LEDs 5 are arranged along common sides 15 in four rows andthree columns next to each other. The thick edges in FIG. 70A centersurround modules 9 grouped in this way, which can combine a plurality ofcomponents 5. In this way, two modules 9 a are created, each groupingtogether three μ-LED 5. Furthermore, two modules 9 b with two μ-LEDSeach and two modules 9 c with one μ-ED each are created.

FIG. 70B shows an illustration of the modules and μ-LEDs after transferto the final carrier 3. 6 columns and rows can be seen on the finalcarrier 3, whereby the number of columns and rows can of course bechosen at will. The module arrangement is chosen so that there is nofurther distance between the modules, i.e. the components are closetogether. However, modules are selected which do not completely fit intothis matrix. For example, 2×2 modules could completely cover the endcarrier shown here. However, two modules are configured in such a waythat they are not designed as a 2×2 matrix but as a 2×1 matrix, i.e.they only have three μ-LEDs, so that one position 11 remains unoccupied.When positioning in the above-mentioned way, two positions 11 thusremain free, whereby the position of these in turn depends on thepositioning of the respective module. The left of the two free positionsis occupied by a sensor element 13. In the version shown, only oneposition is already occupied. In embodiments, however, the sensorelement can also consist of two individual or several elements, whichare then divided between the unoccupied positions.

FIG. 70B thus shows a large number of μ-LED 5, which are groupedtogether in the form of modules 9 and arranged on the end carrier 3. Inthis way, a single full-surface target matrix 1 is equipped. For aμ-display, modules 9 are designed and combined as subpixels. Modules 9for the three different colors red, green and blue are created andarranged next to each other in such a way that they together create apixel (picture element) as subpixels. Then the picture elements arearranged along the target matrix 1 in rows and columns. By usingredundant μ-LEDs, sensor elements can also be positioned in some placesinstead of redundant subpixels.

FIG. 70C shows a representation of an arrangement of a large number offull-surface target matrices 1.

In contrast to FIG. 70B, a large number of full-surface individualtarget matrices 1 are used, each of which can also comprise a largenumber of modules 9 according to FIG. 70B. For a clear description ofFIG. 70C, each single full-surface target matrix 1 comprise only tworows and two columns. Here, the target matrices 1 comprise the sameuniform size in the area. Alternatively, the target matrices 1 cancreate areas of different sizes. In this way, a display device can beflexibly adapted to a particular application.

For example, in the upper left target matrix 1, a module 9 covers allthe vacant positions in target matrix 1. To the right of it, only onemodule 9 is formed with a component 5 in target matrix 1, leaving threepositions 11 unoccupied. Below this, two components 5 form a module 9,leaving two positions 11 unoccupied. A module 9 is positioned in thetarget matrix 1 at the bottom left, consisting of three components 5,whereby only one position 11 remains unoccupied. For example, sensorelements 13 can be formed at least partially at the unoccupied positions11. Three of the four above-mentioned target matrices 1 can each havecomponents 5 for one color red, green and blue and together form apicture element. This picture element can be repeated horizontally andvertically along the first carrier or end carrier 3 so that a displayfunction can be provided. Since a homogeneous radiation of thesub-pixels is generally desired, they are preferably equipped with thesame modules 9 for each color. The fourth target matrix 1 canalternatively be completely equipped with sensor elements 13.

The distancesa and c for respective distances of the target matrices 1in a row and the distance b as an example for a distance of the targetmatrices 1 in a column can be selected according to the desiredresolution of the display. This also applies to the distances to theedges of the first carrier or end carrier 3. The distancesa and b, oraandc, or b and c or a, b and c can be the same. Likewise, the distancesaand b and c can be whole multiples of the spatial extension of acomponent 5 or the distance of the components 5 to each other.

FIG. 70D shows examples of different contact possibilities forelectrical contacting of μ-LED modules on a backplane or othersubstrate. In M1 a contact panel M1 with two areas KB1 and KB2 is shown,which are suitable for two single base modules. The base modules can beplaced on the surface individually or also in combination. Contact panelM1′ expands the contact area KB3. This allows a μ-LED module comprisingtwo connected base modules with shallow mesa etching to be placed andcontrolled together. Panels Ml″ are similar to Panel M1′, but onlycontact areas are provided for one base module. In Panel M2 a μ-LEDmodule is shown, which is arranged above the contact areas. Panel M1′″illustrates an area where a common connection is provided. q

FIG. 70E shows a section of a partially equipped backplane or plane toillustrate some aspects of this. As already mentioned, the μ-LEDs can bemanufactured as an array in rows and columns. This allows the assemblyof several μ-LED modules and modules with different colors. This isshown in FIG. 70E. The section shows a red module rM in direct top view.It is manufactured from a 6×1 module according to the proposed principleand is mounted and contacted on the plane. Adjacent to the red module isa blue module bM in a kind of sectional view to illustrate the differentcontacts. Contacts connected together are marked with K. In thiscontext, the term “common” should be understood to mean that thesecontacts have the same potential as at least some other adjacentcontacts. Accordingly, a common contact area AB4 is applied on theplane. This always contacts contacts K of several base modules as shown.Further contacts Kb are used for individual control of each base module.Consequently, a total of 5 contact areas must be formed on the plane inorder to control 4 base modules individually. As shown in theillustration, the jointly used contact areas can thus also be usedjointly by μ-LED modules of different colors.

FIG. 71 finally shows another aspect of the transfer process. Byperiodically arranging and organizing the μ-LED modules into basemodules, after a separation of μ-LED modules in the desired way, themodules can be transferred using the twofold transfer process presentedin this application. FIG. 71 shows a transfer arrangement 20 with twocushions 22 whose size corresponds to the distance between the basemodules.

In addition to the production of monolithic pixel arrays, μ-LEDs canalso be separately applied to a carrier board and subsequentlycontacted. FIG. 72 shows an embodiment of a pixel module for differentmounts 10 with some aspects according to the proposed principle. Module10 comprises a body 2 with a first main surface 3, a total of four sidesurfaces 11 and a second main surface, not shown here in this view,which forms the bottom. Body 2 is made of, for example, silicon oranother semiconductor material. In some embodiments, however, the bodycan also be formed from another material, conductive or non-conductive.The second main surface is arranged parallel to the first main surface 3and thus forms the underside of the module and body 2. The side surfacesare diagonal to the first main surface or upper side of the body, thusforming a truncated pyramid as shown. Thus, as shown in FIG. 74, anangle α between the first main surface and the side surfaces shows morethan 90°, while the angle β between the second main surface 5 and theside surfaces is less than 90°.

Referring again to FIG. 72, the upper surface 3 comprises an insulatinglayer 22, which is arranged in the middle. In this example, theinsulation layer does not extend completely over the first main surface,but a free area remains at the corners. Several contact pads 14 a to 14c are now arranged on the insulation layer. Each contact pad 14 a to 14c is connected to a contact bar 12 a to 12 c, the width of which issmaller than the actual contact pad as shown. The contact pads 12 a to12 c are also insulated from body 2 of the module. Continuations 13 a to13 c of the contact bars are now attached to the side faces 11 of thebody. As contact tabs, these are in turn much wider on the side surfacethan the contact bars 12 a to 12 c. This increases the possible contactarea on the side faces, allowing greater positioning tolerance andgreater flexibility in contacting.

One μ-LED with vertical design is arranged on each of the contact pads14 a to 14 c. These are configured to emit light in differentwavelengths, for example red, green and blue light. The μ-LEDs comprisean edge length of a few μm, for example 5 μm, and are therefore slightlysmaller than the contact pads 1 a to 14 c. The latter are also spacedapart from each other on surface 3, so that a slight offset is possiblewhen positioning the μ-LEDs without restricting the functionality ofmodule 10. The μ-LEDs are designed as vertical μ-LEDs, i.e. theycomprise one electrical contact each on their bottom and top side. Thecontact on the bottom side is electrically connected to the contact pad.

On the upper side, a transparent conductive layer 21 forms a commoncontact pad for the three μ-LEDs and leads to a fourth contact bar 12 d.This is excellent, as it forms the common connection for all threeμ-LEDs. In the embodiment, it is significantly wider and thicker thanthe contact bars 12 a to 12 c. This enables visual identification,making it easier to transfer and position the μ-LED modules correctlyfor connection. The contact bar is electrically connected to a contacttab 13 d on the last side surface.

With the contact tabs on the side surface, the module or the μ-LEDs canbe electrically contacted if the module is inserted into a matrix orsimilar. FIG. 73 also shows another aspect, which increases the possibleapplications of the module. Several contact pads 15 a to 15 d arearranged on the underside of the module, which are electricallyconnected to the contact tabs 13 a to 13 d. The contact pads on theunderside can be configured in different ways and can thus be adapted tothe requirements of different applications. In the example, the contactpads 14 a to 14 d are substantially rectangular.

FIG. 74 shows a section through the μ-LED module along the X-X-axis inFIG. 73. The bevelled side faces are clearly visible. These include anangle a greater than 90° with the first main surface, i.e. the top ofthe module. For example, the angle can be between 100° and 150°,especially in the range 110° to 130°. The angle depends on themanufacturing process and the parameters used for production, asexplained in detail below. Accordingly, the angle β is less than 90°.The contact tabs and bars form a continuous metallization. The thicknessof the module body is in the range of 10 μm to 100 μm, the metallizationhas a thickness in the range of some 100 nm to approx. 10 μm. Thisallows the module itself to be kept quite flat, but the body itself isstable enough.

FIG. 75 shows a top view of a further embodiment of the μ-LED moduleaccording to the proposed principle, from which further aspects can beseen. In this embodiment, the module with the module body is equippedwith only two μ-LEDs 20 and additionally a further semiconductor chip 30containing integrated circuits. In this version, the μ-LEDs areconfigured as horizontal flip-chips, whose underside, which cannot beseen, comprises the two contacts. The μ-LEDs are mechanically andelectrically connected to the contact bars 12. Each μ-LED is thusconnected to two contact bars 12, some of which are guided tocorresponding contact tabs on the side surfaces. In addition, somecontact tabs are arranged on the top side of the module, thus formingfurther contact pads. The IC chip 30 is connected to contact tabs on oneside of the module body via its own contact bars.

In this embodiment, the individual contact bars do not run in a straightline to the side surfaces. Instead, the embodiment shows a rewiring inwhich contact bars are used that run along the surface and/or the sidesurfaces in order to electrically connect the chip 30 as well as thecomponents 20. The contact tabs 13′ along the side face are placedsubstantially parallel to the edge of the side face, i.e. they run alongthe side edge. This increases the effective contact area with externalcontacts. The module can thus also be easily offset or placed withgreater placement tolerance on a matrix, display or similar.

In a side view according to FIG. 76, this aspect is clarified onceagain. It shows a combination of contact tabs on one side surface and acontact pad 15 on the bottom of the module. The contact tabs 13′ areplaced on the side face, but at different heights.

FIG. 77A shows an example of further processing of a μ-LED moduleaccording to the proposed principle. Module 10 is manufactured in aseparate process and then placed on a carrier in a separate step.Carrier 50 comprises a large number of signal, control and power lines,of which line 56 is shown here as an example. In addition, carrier 50also includes integrated circuits 55, buffers and similar. In thisexample, the module is placed on the carrier directly next to line 56and fixed there. In order to achieve an electrical contact andconnection between pad 56 and contact tab 13, these two are connected ina further step. This is shown in FIG. 77B. Contact pad 56 is attached tocontact tab 13 by reflow or other soldering method. Material 57 is aconductive metal. This not only creates an electrically conductiveconnection, but also fixes the module mechanically to the carrier. Insuch a case, additional fastening of the module body to the carrier isnot necessary.

FIG. 77C shows various contact options in this context. In the upperillustration of FIG. 77C, the module body is placed on contact pads 56 bon carrier 50 in such a way that the contact pads on the underside ofthe module body overlap with them. A firm connection between the twopads is created by means of paste, reflow or other methods afterheating. This requires an exact positioning of the module on thecarrier.

In the lower illustration of FIG. 77C, a similar shape is shown as inFIG. 77B. The contact tab on the side face of module body 2 is attachedto carrier 50 by soldering a wire to the carrier 50. In one case, thislead 56 on the carrier is designed so that it also partially overlapswith the contact pad on the underside of the module body. This makes theelectrical connection even more reliable. At the same time, thisembodiment is somewhat less sensitive to positioning fluctuations, asthe lines on carrier 50 can be made larger and at the same time, aconnection is improved with the additional solder. To ensure that thesolder does not create a short circuit, the area 50 should be insulatedapart from the contact area of line 56. However, it is advisable toconfigure the area around the contact of line 56 in such a way thatsolder also reaches the line, thus improving the electrical connection.

FIGS. 78A and 78B show an example of another version of a special modulebody. In this module, body 2 is configured with a central recess inwhich the components 20 and 30 are arranged. This allows the height ofthe module to be further reduced. In addition, the edge area of themodule body can serve as a mounting for optical elements such as lensesand the like. The contact lines to the optical semiconductor components20 and 30 run along the bottom of the recess and the side surface. Asshown in FIG. 78B, the side surface of the recess is sloped.

To make contact, the leads 80 are routed along the inner side face, overthe main face along the outer side face, to the rear contact pad 15. Inthis illustration, the outer side surface is substantially vertical.However, this is not necessary, in some configurations this side surfacecan also be bevelled in the same way as in the previous embodiments.

The module body also has a through hole or via 60, which extends throughthe material of the module body in the recess. The via is filled with ametal for contacting, which is also insulated from the body. Thiscombination of vias and contact tabs and pads creates a very flexibleconcept that can produce modules for a variety of technologies andconnection variants in a standardized way.

FIGS. 79A and 79B continue this principle. In both FIGS. 79A and 79B,module body 2 also comprises a recess or notch, but the recess or notchis in the bottom of the module body. The μ-LEDs are located on the upperside of module body 2. In the examples, several vias 60 are providedwhich extend through the material of body 2 and are connected tocontacts of components 20. On the side facing away from the components,i.e. in the recess, contact bars 12 are now provided which connect thevia 60 in an electrically conductive manner and lead along the recess toridges 80 on the side surfaces. The bars 80 on the inner side surface ofthe recess are then connected to contact pads 15 on the bottom side.

In contrast to FIG. 79A, the lower contact pads in the FIG. 79B versionare contacted via the outer surfaces of the module body. Both versionscan also be combined with each other, i.e. through-plated holes areprovided as well as contact lines, which are electrically connected tocontact tabs on the outer side surface and/or contact pads. Due to theincreased surface area of the module body, a specifically adapted wiringcan be carried out, the flexibility for wiring is significantlyincreased. The embodiment of FIGS. 79A and 79B makes it possible, whenpositioning the module, to provide 10 additional circuits on the carrierwhose position is in the recess. This results in a higher integrationdensity.

FIG. 80 shows in this context an example of a manufacturing process fora module according to the proposed principle. It should be noted in thiscontext that various techniques disclosed in this application are usedfor the production. One component, however, is a structured membranewafer as shown in step S1. This is done by providing the membrane waferand structuring it by etching in such a way that V-shaped recesses andtrenches are formed in sections. A plan view of such a structuredmembrane wafer is shown in FIG. 84.

In step S2, contact pads and leads or contact bars and tabs aregenerated on the structured membrane wafer. For this purpose, aphotomask is applied and, for example, the metallic leads are formed byMOCVD. If necessary, previously formed isolated vias can also be filledwith a metallization in this step. In step S3, the μ-LEDs are now placedon the contact pads and connected to them.

In step S4, the membrane wafer is rebonded onto an auxiliary carrier sothat the back of the membrane wafer is exposed. Then in step S5, this isetched back to the trenches. This allows the modules to be separated sothat each module now carries the intended number of μ-LEDs. In theexemplary step S5, it is a component. Alternatively, step S6 can also becarried out, in which etching is also carried out, but several μ-LEDsare now combined to provide a module, which is similar to the previousexamples. There is no limit to the number of μ-LEDs and theirpositioning, but depends on the requirements and the later use. In alast optional step, contact pads are attached to the underside of themodule body and these are electrically connected to the contact tabs onthe side surface.

FIG. 81 shows a perspective view of the module of FIG. 72 after it hasbeen placed on a carrier. The carrier includes several supply lines andcontrol lines. A supply line 92 is connected to the common contact pad13 d via a contact bar 90 b. Contact pad 13 b is designed as a topcontact and connects the top contacts of the respective vertical μ-LEDsto a common connector. A further supply line 91 contacts the contact pad13 a on the side surface of the module body via bar 90 and thus connectsa connection of the red μ-LED. The slanted side surfaces ensure a secureelectrical connection between bar 90 or 90 b and the respective contacttabs. In addition, the module is attached using a soldering process, inwhich the bars 90 are soldered to the tabs 13 a to 13 d. Since thecontact tabs 13 a to 13 d cover a relatively large part of therespective side surface, the requirements for positioning accuracy aresomewhat lower.

FIG. 82A shows a top view of a module with three μ-LEDs of differentcolors with metal bars 12 a to 12 d on the surface of the module bodyfor contacting three μ-LEDs. These form a subpixel of a pixel and aredesigned as SMT μ-LEDs. They have a contact pad on their underside oneach side and thus form horizontal LEDs. Schematically, the μ-LEDs 20are represented by the dotted line. Their contact pads are arrangedlaterally. For perfect contacting they are thus connected on one side toone of the contact bar 12 a to 12 c. In addition, a common contact isrealized with the bar 12 d and the metallization there. Each of the bars12 a to 12 c leads into one of the corners and to a contact tab 13 a to13 c along one corner.

FIG. 82B shows an alternative embodiment in which the μ-LED components20 are vertical μ-LEDs with one contact pad on the bottom and another onthe top. In this example, the contact pads 14 a to 14 c are larger andhave essentially the same dimensions as the μ-LED. The latter is placedon the contact pad and electrically connected to it. Contact bars 12 ato 12 c also connect the respective corner tabs 13 a to 13 c with thecontact pads. The fourth common contact bar 12 d is wide and serves tocontact the top side of the μ-LEDs 20 via a transparent electricallyconductive material.

FIG. 83 shows the underside of the version according to FIG. 82A.Contact pads 15 on the underside are contacted by the contact tabs 13 ato 13 d on the side surface. These are designed to have a relativelylarge surface area. The cut-out also shows a side view. In one design,one of the contacts is larger than the other and forms the connectionfor the common contact lead 12 d on the top side.

In addition to the production of a monolithic display, some applicationsand designs also involve the transfer and attachment of μ-LEDs to acarrier substrate and contact areas there. In order to reduce the errorrate during a transfer and the following process steps, the followingpropose examples and designs show for a pixel array with redundantμ-LEDs positions. Those can assembled with components if needed. TheFIGS. 85A to 85C show a top view of the contacts 13 provided for onepixel 11 on a substrate 15. The substrate 15 comprise several suchcontacts 13 for further pixels, which are arranged in field or arrayfashion. After an assembly with subpixels, as shown below, a pixel fieldor pixel array results, which can be arranged in a display, for example.

The contacts 13 can be divided into a set 17 of primary contacts 17 a,17 b and 17 c and a set 19 of replacement contacts 19 a, 19 b and 19 c.Each of the contacts 13 can be equipped with a subpixel, for example aμ-LED. FIG. 85A shows the unpopulated state.

In a first assembly step the pixels 11 of the substrate 15 are assembledin such a way that for each pixel 11 the primary contacts 17 a-17 c areassembled with one subpixel 21 a, 21 b, 21 c each, while the sparecontacts 19 a, 19 b, 19 c remain free. The subpixel 21 a can be a μ-LED,for example, which can emit light in the red spectral range. Thesubpixel 21 b, for example, can be a μ-LED that can emit light in thegreen spectral range. The subpixel 21 c, for example, can be a μ-LEDthat can emit light in the blue spectral range. Pixel 11 thus has a setof RGB subpixels 21 a-21 c after the first assembly, as FIG. 85B shows.

After the first placement, the subpixels 21 a-21 c can be checked forerrors. For example, subpixel 21 c can be identified as faulty.

In a second assembly step, the replacement sub-pixel 19 c can beequipped with a replacement sub-pixel 23, which can be a μ-LED emittingin the blue spectral range. The replacement subpixel 23 thus replacesthe faulty subpixel 21 c, which can be left on the primary contact 17 c.

In the case of substrate 15 as shown in FIGS. 85A to 85C, each pixel 11has a respective, assigned replacement contact 19 a-19 c for eachprimary contact 17 a, 17 b, 17 c. The substrate 15 thus allows eachsub-pixel 21 a-21 c on a primary contact 17 a-17 c to be replaced by asubstitute sub-pixel on a substitute contact 19 a-19 c.

In contrast, as shown in FIGS. 86A to 86C, the substrate 15 comprisesthree primary contacts 17 a, 17 b and 17 c per pixel 11 and only onereplacement contact 19 a, which makes it possible to replace a faultysubpixel on one of the primary contacts 17 a to 17 c. Additionalcircuitry measures shall be provided to ensure that the pixel with itssubpixel on the secondary contact is addressed in the correct color.

FIG. 86A again shows a top view of the contacts 13 for a pixel 11 inunpopulated condition. As FIG. 86B shows, after a first assembly step,the primary contacts 17 a-c are equipped with subpixels 21 a-21 c, whichin turn can be μ-LEDs for the primary colors red, green and blue.

In a subsequent step, for example, subpixel 21 a can be identified asfaulty. As a replacement for this faulty subpixel, a replacementsubpixel 23 can be placed on the replacement contact 19 a as shown inFIG. 86C, which emits light of the same color as subpixel 21 a if itwere faultless.

FIGS. 87A to 87C show a respective top view of a substrate 15, in whicha set of primary contacts is provided for a respective pixel 11,comprising six primary contacts 17 a, 17 b, 17 c, 17 d, 17 e and 17 f.In addition, the substrate 15 comprise three spare contacts 19 a, 19 b,19 c for a respective pixel 11. FIG. 87A shows the primary andreplacement contacts in an unpopulated state.

In a first assembly step as shown in FIG. 87B, the primary contacts 17a-17 f are assembled with respective subpixels 21 a-21 f. Two subpixelsof each primary color red, green and blue can be provided. This providesdouble redundancy for each of the primary colors red, green and blue. Inaddition, the provision of 2 subpixels per color allows a more precisegradation of brightness and thus an improved brightness resolution.Despite the redundancy, subpixels 21 a-21 f can be checked for errors.For example, if it turns out that both subpixels 21 c and subpixels 21f, which emit light of the same color, are faulty, a replacementsubpixel 23 can be provided on the replacement contact 19 c to replacethe two faulty subpixels 21 c and 21 f.

The primary contacts 17 a-17 f as well as the spare contacts 19 a-19 ccan be used for the electrical contacting of the subpixels 21 a-21 f, 23arranged on them. The subpixels can be μ-LEDs in particular, asexplained above.

The described manufacturing method is particularly suitable for theproduction of pixel fields for μ-displays, which use μ-LEDs as subpixelswith horizontal flip-chip design. In this design, p- and n-contact arelocated on the bottom side of each μ-LED. This allows an electro-opticalcharacterization of the individual μ-LEDs before further process stepsprevent the substrate 15 from being refilled. The describedmanufacturing process is also advantageous for pixel arrays withvertical μ-LED chips. Depending on the test method used to finddefective subpixels, the redundant replacement contacts 19 a-19 c can bere-equipped in different steps of the manufacturing process. Attentionshould be paid to a further processing option for the electricalcontacting of the replenished replacement contacts 19 a-19 c or thereplacement subpixels 23.

With regard to the electrical connection of the primary contacts 17 a-17f and the replacement contacts 19 a-19 c there are different approaches.For example, with reference to FIG. 87, the redundant contacts 21 a and21 d or 21 b and 21 e or 21 c and 21 f can be integrated into the samerespective subpixel circuit. The redundancy can thus only refer to theprimary contacts for the subpixels, but not necessarily to a circuit forcontrolling the subpixels.

The spare contacts 19 a-19 c can be wired in such a way that they can becontrolled after an assembly instead of a subpixel identified as faulty.

The primary and replacement contacts assigned to each other can also beconnected in parallel, whereby a supply line to a primary contact isdisconnected if the sub-pixel arranged on it proves to be faulty and thereplacement contact is equipped with a replacement sub-pixel.

As can be seen with reference to FIGS. 86A to 86C, at least one sparecontact 19 a may also be provided as a redundant placement facility forthe sub-pixels on primary contacts 17 a-17 c, the spare contact 19 aallowing for a placement of a spare subpixel regardless of the color ofthe emitted light. This redundant spare contact 19 a can be connectedlike a fourth subpixel. A programming of the control of the replacementcontact should be adapted to the population of the replacement contact19 a depending on the color of the subpixel identified as defective onone of the primary contacts 17 a-17 c.

In the following, some concepts for measures to improve a transfer inthe form of an improved mass transfer printing process are presented.Background of the process is a transport of μ-LEDs of a wafer onto acarrier surface of a display. There, the individual μ-LEDs are fixed andattached and electrically connected. On the one hand, the dimensions ofthe individual μ-LEDs are in the range of only a few [μm]n, on the otherhand a large number of these μ-LEDs have to be transferred locally atthe same time. Often several million of such microstructures have to betransferred from a large number of wafers to a common carrier surface.

In the example shown here in FIG. 27A, a wafer 12 is initially plannedon which epitaxial layers have been created by various semiconductormanufacturing processes, from which the individual μ-LEDs 16 are thenformed. In some aspects, the μ-LEDs can emit different colors andwavelengths during operation. This is indicated here by the differentshades. The μ-LEDs are flat at least on their underside and/or topsurface to allow for easy mounting and transport, for example. As partof the manufacturing process, the μ-LEDs 16 can be mechanicallyseparated from wafer 12. This is done by removing a so-calledsacrificial layer (see for example FIGS. 24A to 24D as well as 22J, 23Jand 25J), if necessary supplemented by one or more release layers.

FIG. 27B shows how an elastomer stamp 18 is moved vertically from abovetowards the wafer 12 and adheres to a surface of the μ-LEDs 16 by meansof a suitable surface structure of the elastomer stamp 18. For example,a maximum tensile force can be proportional to a size of the surface ofthe μ-LED 16. Adhesion can be created by silicone materials, forexample, especially by so-called PDMS elastomers. Due to the separationof the μ-LEDs 16 from wafer 12, the μ-LEDs in their plurality can belifted off wafer 12 together, whereby they adhere to the elastomer stamp18. This elastomer stamp 18 is now moved in a transfer movement awayfrom wafer 12 to a carrier surface 14 of a display mounted next to it,for example. This can be done, for example, with the aid of a transfertool, whereby the elas-tomer stamp 18 can be regarded as part of such atool.

In FIG. 27C, the elastomer punch 18 is now initially located above thecarrier surface 14 and is lowered onto a surface of the carrier surface14 in a lowering movement. In this process, the underside of the μ-LEDs16 comes into mechanical contact with the carrier surface 14. In asubsequent step, as shown in FIG. 27D, the μ-LEDs 16 are detached fromthe elastomer stamp 18. The elastomer stamp 18 is then moved upwards,for example to start a new transfer cycle. The μ-LEDs 16 can, forexample, be permanently attached to the carrier surface 14 by anadhesive process.

The steps shown in FIGS. 27A to 27D indicate that due to the high numberof μ-LEDs 16, reliable and accurate placement in the shortest possibletime is desirable. Especially when the μ-LEDs 16 are picked up by thestamp 18, it may be desirable to keep the occurring forces low on theone hand and to achieve a reliable positioning and holding of the μ-LEDs16 on wafer 12 on the other hand. In particular, avoiding fluctuationsin the adhesive force or excessive adhesive forces on the wafer and/oron the stamp can bring about significant improvements here.

FIGS. 22A to 22J show a first example of a process for manufacturing aμ-LED with a μ-LED supporting holding structure. The manufacturingprocess of the μ-LED is simplified. It should be noted in this contextthat the process can be supplemented and extended with the measuresdisclosed here.

FIG. 22A shows a step in which a sacrificial AlGaAs sacrificial layer isfirst applied to a substrate 3, which here shows GaAs. A functionallayer stack 1 is then epitaxially grown on this sacrificial layer stack,which thus has at least one quantum well or another optically activestructure 13. In addition, the layer stack comprises two layers 15 and17, which are doped differently. The n-doped semiconductor layer 15 ishere attached to the sacrificial layer 11. A first electricallyconductive contact layer 5 is then deposited on a side of the functionallayer stack 1 facing away from the substrate 3. This may, for example,contain ITO (indium tin oxide).

FIG. 22B shows a step in which a first lithographic processing iscarried out on the main surface side of the functional layer stack 1 onthe first electrically conductive contact layer 5, which is turned awayfrom the substrate 3. In particular, a first masking layer 19 is appliedto the first electrically conductive contact layer 5, whereby an area ofthe first electrically conductive contact layer 5 remains uncovered bythe first masking layer 19 in order to create a holding structure 9.From this side of the layer sequence, the first electrically conductivecontact layer 5, the functional layer stack 1, the sacrificial layer 11and a part of the substrate 3 can then be etched out in the uncoveredarea so that the recess shown in cross-section is formed. The sidewallsare very steep or fall down essentially vertically.

FIG. 22C shows a step in which a support structure 9 is formed in theetched out area of the layer sequence. This is done by depositingmaterial from a gas phase, which extends over the masking 19 and fillsthe trench until a small recess remains in the material of the web 9 atthe level of the masking layer. The recess can be production-related andoptionally omitted, for example by applying material until the recess iscompletely filled. A too thick layer of material on masking 9 can bethinned again by CMP or other methods.

FIG. 22D shows another aspect after the material on masking layer 19 andlayer 9 itself has been removed. A second photomask 21 is then appliedand patterned in a second area to provide access to the sacrificiallayer. The area between the holding structure and the patterning formsthe μ-LED. After patterning, etching is again carried out through layers5 and 1 to the sacrificial layer 11. This results in the structure shownin FIG. 22J. Here the etching process can form a trench or similar todefine the dimensions of the μ-LED.

FIG. 22E shows the structure after the etching process, in which thesacrificial layer 11 is removed from the layer sequence, especially bywet chemical etching. The functional layer stack 1 is then supported bythe holding structure 9, which is attached to the substrate 3. In afinal step, a second electrically conductive contact layer 7 is attachedto the functional layer stack 1 on the side of the functional layerstack 1 facing the substrate 3 in the area of the removed sacrificiallayer 11. The material of the second electrically conductive contactlayer 7 may contain ITO (indium tin oxide). In the area where thesacrificial material has been etched away, the second electricallyconductive contact layer 7 can be applied by sputtering, see FIG. 22F.In this way, the space between the substrate 3 and the functional layerstack 1 can be accessed. In addition, when the second electricallyconductive contact layer 7 is applied, flanks of the functional layerstack 1 and an area of the exposed area of substrate 3 can be covered.It is also possible to deposition from the gas phase, electroplating orother techniques.

After finishing the contacts 7 on the underside of the structure, theelectrically conductive material is removed again on the flank andespecially in the area of the trench. The structure thus produced isshown in FIG. 22G. FIG. 22H shows a step in which the flanks of thefunctional layer stack 1 that are free of electrically conductivematerial are covered by a passivation layer 23. This is optional. Thesecond masking layer 21 has also been removed. A further passivationlayer 25 can also be created on the substrate 3 covered withelectrically conductive material of the second electrically conductivecontact layer 7.

The structure shown in this way can now be broken away from the holdingstructure using the stamp described above or another transfer tool. Theflanks of layer stack 1 are also covered by a passivation layer 23. FIG.22J again shows the step of breaking off the μ-LED thus produced as atop view. The large arrow is intended to show the break-off from aholding structure 9 and the jagged area is intended to represent a breakpoint 29.

A further example is shown in FIGS. 23A to 23J. FIGS. 23A to 23F showsteps identical to those in FIGS. 22A to 22F. In contrast to the stepsshown in FIG. 22G, FIG. 23G involves removing the electricallyconductive material deposited on the flanks of the functional layerstack 1. Then, before or instead of passivation, a metal is deposited onthe flanks and diffused. This material can be Zn in particular. Itdiffuses into the edge area of the layer stack and produces a change inthe band structure there, so that charge carriers are kept away fromthis area of high defect density. Accordingly, the non-radiativerecombination of charge carriers in the functional layer stack isreduced in this way. This is followed by the same steps as in FIGS. 22Hto 22J as shown in FIGS. 23H to 23J.

FIGS. 24A to 24I show a third embodiment of a proposed process formanufacturing a μ-LED with a holding structure.

FIG. 24A shows a step in which a functional layer stack 1 wasepitaxially deposited on a GaAs substrate 3 over a sacrificial layer 11of AlGaAs. Between the functional layer stack 1 and the sacrificiallayer 11, a second supporting layer 24 is also epitaxially formed, whichcontains, for example, InGaAlP and is relatively thin compared to thesacrificial layer 11. Similar to the previous explanations, the dopedsemiconductor layer of layer stack 1, which is adjacent to layer 24 andthe sacrificial layer, is n-doped. The second semiconductor layer 17 isp-doped.

A first electrically conductive contact layer 5 not shown here issubsequently applied to a side of the functional layer stack 1 remotefrom the substrate 3, especially the main surface side. This can thenhave ITO (indium tin oxide), for example.

FIG. 24B shows a step in which a first lithographic processing iscarried out on the main surface side of a functional layer stack 1 thatfaces away from a substrate 3. For this purpose, a first masking layer19 is applied to the second semiconductor layer 17 of the functionallayer stack 1, whereby, for the creation of a holding structure 9, outeredge regions of the functional layer stack 1 remain uncovered by thefirst masking layer 19. From this side of the layer sequence, thefunctional layer stack 1, the second supporting layer 24 and thesacrificial layer 11 can be removed, in particular etched away by meansof ICP (inductively coupled plasma etching), in these uncovered edgeregions up to the substrate 3. Finally, the first masking layer 19, isremoved again. The trench thus formed can extend around all sides of thebody, thus forming one or more μ-LED structures separated by trenches.

FIG. 24C represents a further step in the process, in which a firstsupport layer 20 is formed on the substrate 3, on exposed edge areas ofthe layer sequence and on a main surface of the μ-LED 1 facing away fromthe substrate 3 to provide a support structure 9. The material of thesupport layer 20, which is deposited from a gas phase and epitaxiallygrown, for example, has InGaAlP. The support layer 20 envelops the layersequence at least on one side up to substrate 3, it thus extends fromthe second main surface side over at least one side flank to substrate.Finally, a second masking layer 21 is applied to the main surface of thefirst support layer 20 facing away from substrate 3. An outer edgeregion of the layer sequence remains uncovered by the second maskinglayer 21.

FIG. 24D shows a step in which an outer edge region uncovered by thesecond masking layer 21 of the layer stack 1, the second support layer24 and the sacrificial layer 11 up to the substrate 3 has been removed,in particular by etching. In this way, an access to the sacrificiallayer 11 will be formed from this side of the layer sequence. The areascovered by the second masking layer 21 remain intact even after thesecond masking layer 21 has been removed in FIG. 24D.

FIG. 24E shows a step in which the sacrificial layer 11 is removed fromthe layer sequence, in particular by wet chemical etching. The removalis performed from the outer edge of the layer sequence exposed in step24 D. The functional layer stack 1 is then supported by the firstsupport layer 20 and the second support layer 24, the first supportlayer 20 being attached to the substrate 3. In this way, a supportstructure 9 is provided which supports the functional layer stack 1,without the sacrificial layer 11.

FIG. 24F shows the structure after which a first electrically conductivecontact layer 5 and a second electrically conductive contact layer 7 areformed. An electrically conductive layer is formed, which is attached tothe side facing away from the substrate 3 on the first supporting layer20, which is attached to the functional layer stack 1 in a supportingand electrically conductive manner. The electrically conductive layer isalso applied to the side of the functional layer stack 1 facing thesubstrate 3 in the area of the removed sacrificial layer 11 on thesecond supporting layer 24. The material of the electrically conductivelayer may contain ITO (indium tin oxide). Especially in the area wherethe sacrificial layer 11 was etched away, the electrically conductivelayer can be applied by sputtering. In this way, a space between thesubstrate 3 and the functional layer stack 1 is easily accessible. Whenthe electrically conductive layer is applied, flanks of the functionallayer stack 1 and at least part of the exposed area of substrate 3 canalso be covered.

FIG. 24G shows a step in which the electrically conductive materialdeposited on the flanks of the functional layer stack 1 is at leastpartially removed, in particular etched away, in such a way that thefirst electrically conductive contact layer 5 on the side facing awayfrom the substrate 3 is produced electrically separately from the secondelectrically conductive contact layer 7 on the side of the functionallayer stack 1 facing the substrate 3. In this way, a contactedfunctional layer stack 1 is formed.

For this purpose, a third masking layer 31 is first applied to the firstbase layer 20. This third masking layer 31 leaves edges to the flanks ofthe functional layer stack uncovered. This third masking layer 31 coversedge areas of the first support layer 20 that are attached to thesubstrate 3. By means of removal, in particular by etching, firstly thefirst and second contact layers 5 and 7 are electrically separated fromeach other and the support layer 20 is mechanically reinforced by thefirst contact layer 5 in such a way that a retaining structure 9 isadditionally mechanically reinforced.

FIG. 24H shows a step where the third masking layer 31 has been removed.The functional layer stack 1 is attached to the substrate 3 by aretaining structure 9. For attachment, the first support layer 20,reinforced by the first electrically conductive contact layer 5,interacts with the functional layer stack 1, stabilized and protected bythe second support layer 24. By means of a lifting head 27, thecontacted—i.e. indirectly coated with the contact layers 5 and7—functional layer stack 1 can be lifted off and thereby broken off fromthe holding structure 9. Reference mark 29 denotes a predeterminedbreaking point at which an electronic component or a contactedfunctional layer stack 1 can be detached from a substrate 3.

FIG. 24I again shows a step of breaking a layer stack 1, which haselectrical contacts and provides at least one function, in contrast tothe cross-sections in FIGS. 24A to 24H, this time as a top view. Thelarge arrow is intended to show the breaking off of a retainingstructure 9 and the jagged point is intended to represent a break point29. A detachable electronic component, in particular a detachablemicro-light-emitting diode, may be attached to several retainingstructures 9, for example, in planar view, at rounded corners of thecomponent.

FIGS. 25A to 25J show a fourth example of a proposed method. FIGS. 25Ato 25D show steps similar to those in the previous example in FIG. 24.

In contrast to FIG. 24E, FIG. 25E shows a step in which only part of thesacrificial layer 11 is removed by wet chemical means. This exposes apart of layer 24 and the contact layer 7 is then applied. The removal isperformed from the outer edge of the layer sequence exposed in step141D. The functional layer stack 1 is then supported by the firstsupport layer 20 and the second support layer 24, with the first supportlayer 20 attacked to the substrate 3. In this way, a support structure 9is provided to support the functional layer stack 1 without the completesacrificial layer 11.

FIG. 25F shows a step in which a first electrically conductive contactlayer 5 and a second electrically conductive contact layer 7 are formedon a sacrificial layer 11, which is only partially removed in FIG. 25E.In this process, an electrically conductive layer 5 is formed, which isattached to the side facing away from the substrate 3 on the firstsupport layer 20, which is attached to the functional layer stack 1 in asupporting and electrically conductive manner. The electricallyconductive layer also extends to the side of the functional layer stack1 facing the substrate 3 in the area of the removed sacrificial layer11. Especially in the area where the sacrificial layer 11 has beenetched away, the electrically conductive layer can be applied bysputtering. In this way, a space between the substrate 3 and thefunctional layer stack 1 is easily accessible. When applying theelectrically conductive layer, flanks of the functional layer stack 1and the exposed area of the substrate 3 can also be covered with theelectrically conductive material.

FIG. 25G shows a step in which the electrically conductive materialdeposited on the flanks of functional layer stack 1 is at leastpartially removed. The first electrically conductive contact layer 5 onthe side facing away from the substrate 3 is thus electrically separatedfrom the second electrically conductive contact layer 7 on the side ofthe functional layer stack 1 facing the substrate 3.

For this purpose, a third masking layer 31 is applied to the first baselayer 20. This third masking layer 31 leaves edges to the flanks of thefunctional layer stack uncovered. This third masking layer 31 coversedge areas of the first support layer 20 that are attached to thesubstrate 3. By means of an etching process, the first and secondcontact layers 5 and 7 are electrically separated from each other.Independently of this, the first contact layer 5 mechanically reinforcesthe support layer 20. The remaining sacrificial layer 11 is retainedduring this step.

FIG. 24H shows the structure after removing the third masking layer 31and the remaining sacrificial layer 11, both of which can be removed byvarious etching processes. The functional layer stack 1 is attached tothe substrate 3 by a retaining structure 9. For attachment, the firstsupport layer 20, reinforced by the first electrically conductivecontact layer 5, interacts with the functional layer stack 1, stabilizedand protected by the second support layer 24. FIG. 25I again shows thepredetermined breaking point 29. FIG. 25J again shows a step of breakinga μ-LED 1 with electrical contacts as a top view. Depending on thedesign, a holding structure can hold several such μ-LEDs so that theycan be lifted off together or one after the other by a transferinstrument.

In the last versions shown here, a breaking edge is formed. Althoughthis is only very narrow, it can still lead to non-radiatingrecombination centers, so that the efficiency of the μ-LED is somewhatreduced. In addition, somewhat higher demands are placed on the transferstamp or transfer technology.

An aspect that leads to a further reduction of the influence ofnon-radiative recombination centers is shown in FIGS. 26A and 26B. Asalready mentioned, the fracture edge often generates recombinationcenters, which leads to an increase in non-radiative recombination inthis area and thus reduces efficiency. After processing thesemiconductor layer sequence, a photomask 23 is now applied andpatterned so that the surface adjacent to the later edge regions isexposed. In contrast, photoresist remains over the area of the lateractive layer or the active region. Subsequently, a dopant, for exampleZn, is deposited on the surface. In the next step, shown in FIG. 26B, adiffusion step is performed. The Zn diffuses through layer 17 andreaches the active region. With suitable process parameters, quantumwell intermixing occurs, provided that the active region is formed byone or more quantum wells. Quantum well intermixing shows a strongchange in the region of the mask edge as explained in this application,so that the course of the band gap is quite steep and resembles a bandgap jump. The increased band gap thus occurs mainly in the edge regionand also in the region 25 a, where the breaking edge is later formed.The breaking edge is thus formed in an area of increased band gap, sothat charge carriers are kept away from the defects caused by the edgeduring operation. After quantum well intermixing has been generated, thedevice can be further processed as described above.

Referring back again to FIGS. 27 and 28, these show a further embodimentof a support structure 10 according to some suggested principles foravoidance of breakage edges and improved liftoff. In principle, thebasic structure corresponds to the diagram in FIG. 27A. In particular,the wafer shown in FIGS. 27A and 27B comprises the wafer structure shownin the followng, whereby FIG. 28 refers to a simplified top view of awafer 12 from a top side. Three μ-LEDs 16 can be seen, which in thisexample are each flat rectangular and arranged next to each other. Othershapes of chips are possible for example hexagonal. On a wafer 12, alarge number of such μ-LEDs 16 can be provided on a surface of 16 or 18inches, for example, arranged side by side.

Prior to a transfer process, these μ-LEDs 16 are mechanically detachablyarranged on wafer 12. This means that they can be removed by a stampingtool 18. In the example shown here, the μ-LEDs 16 are partially detachedfrom wafer 12 on their underside (not visible) and are now held byholding elements 20. The mounting elements, which appear round here dueto the top view, can be columnar or pole-like with, for example, around, angular or elliptical cross-section, made from a carriersubstrate 22 underneath. As shown, the μ-LED 16 shown here in the middleis held in position by a total of three mounting elements 20. The threesupport points in particular make it possible to achieve coplanarity,i.e. an arrangement that is stable from the point of view of thedistribution of forces and is in the same plane as the other μ-LEDs 16.Two of the mounting elements 20 each hold two μ-LEDs 16 at their cornersor edges.

In the following FIGS. 29A to 29D, a vertical sectional view (see line24 in FIG. 28) is shown for various possibilities of designing a supportstructure 10. A wafer 12 or, in general, a carrier material or bondingmaterial serves as the basis for mechanical stabilization and foraccommodating other components such as electrical connections,electronic control elements and the like. A first release layer 26 isarranged vertically above it. The release layer 26 serves to enablecontrolled delamination, i.e. the deliberate and controlled separationof the layers from each other by means of a defined tensile force.Furthermore, such a layer can serve as an etch stop layer to leaveadjacent layers unchanged during an etching process. This can, forexample, replace a breakage process, as it has been used up to now inthe state of the art, with a peeling process in which no disturbingresidues remain on the μ-LED.

A sacrificial Layer 28 is also provided for. The background to this isthat silicon, for example, is used as the material for such layers,which can then be removed in one process step by chemical processes, forexample to separate the μ-LED 16 from the wafer 12 below it. The μ-LED16 also has a contact pad 30, which can have a semiconductor active areasuch as a p-n junction. FIG. 29A and FIG. 29B show the cross-section ofa μ-LED 16 with an epitaxial layer 32 as an example. This epitaxiallayer 32 can also be supplemented by a second release layer 34, which isformed between the sacrificial layer 28 and the epitaxial layer 32. Thissecond release layer 34 can be arranged at different locations dependingon the design variant.

FIGS. 29A and 29B each show a design variant in which a receivingelement 20 as a pole-like, columnar or post-like elevation from wafer 12extends in one piece vertically between two μ-LEDs 16 through thesacrificial layer 28 and ends before the epitaxial layer 32. Here, theepitaxial layer 32 tapers tightly towards the top, thus forming aV-shaped mesa trench 38 (see FIGS. 30 and 31). While in FIG. 29A thesecond release layer 34 extends to a side or partial underside ofcontact pad 30, the second release layer 34 ends horizontally in frontof contact pad 30 with sacrificial layer 28 filling the remaining gap. Agaseous or liquid etching substance can then reach the sacrificial layer28 via the mesa trench 38, i.e. the space between two μ-LEDs 16.

In FIG. 29B, the delamination layer on the exposed surface of thereceiving element is also removed by the etching process.

By controlling the etching process, the removal of the delaminationlayer can be selectively adjusted. For example, the delamination layermay have a significantly lower etch rate than the sacrificial layer 28with respect to the etching process used. This ensures complete removalof the sacrificial layer without overly attacking the delamination layeror the carrier substrate by the etching process. In an alternativeembodiment, which is not shown here, the etching process is also used toetch through the delamination layer and into the carrier substrate. Inother words, the funnel-shaped recess between the two μ-LEDs iscontinued in the receiving element. This results in a V- or U-shapedrecess for the receiving element, leaving two columns on which theμ-LEDs are placed. The depth of such an etch in the receiving elementcan also be set by the process. In general, however, not the entirereceiving element is etched through. Rather, the receiving element isetched only up to half of its height or less, so that sufficientstability of the receiving elements is ensured. In particular, it isensured that the remaining columns do not break when the μ-LEDs areremoved, but that the μ-LED is lifted off by overcoming the adhesiveforce of the delamination layer.

FIGS. 29C and 29D show a further embodiment, particularly with regard tothe design of the mounting element 20. Here, the receiving element 20protrudes in one piece from the plane of wafer 12 through thesacrificial layer 28 to an opposite side of the support structure 10. Inthis case, the pick-up element 20 is tapered at its upper end ordesigned with slanted μ-LED retaining surfaces 36, which can alloweasier lifting of the μ-LEDs 16 while at the same time ensuring a securefit on wafer 12. In FIG. 29D, according to one example, the receivingelement 20 ends vertically before the end of the epitaxial layer 32. Thecontact pad 30 connects the layers inside the μ-LED and especially thelight emitting layer. As shown in FIGS. 29B and 29D, the contact pad 30is the vertically lowermost element in each case and can therefore comeinto direct mechanical and thus electrical contact with an electricalcontact element (not shown) on a support surface of the display ormodule, if necessary without additional bridging solder or conductiveadhesive. A contact pad 30, for example, can have edge lengths in therange of 1-15 μm.

Finally, FIG. 29E shows an embodiment in which the receiving element issignificantly widened and the delamination layer extends completely overthe surface of the receiving element. As shown in FIGS. 29C and 29D,sacrificial layer 28 extends through the funnel-shaped region betweenthe individual μ-LEDs with its epitaxy 32. Each μ-LED comprises anepitaxy whose lateral dimensions are larger on the light-emitting sidethan on the side facing the contact pad 32. In other words, the μ-LEDswiden from the side with the contact pad 32, resulting in an “inverted”V-shape in the shown sectional structure. A further layer 34 is appliedto the surface of the areas of the epitaxial layer 32, especially on thesloping sides forming the funnel and on the surface containing thecontact pad. This serves as an etching stop and, together with thedelamination layer 26, produces a defined adhesive force. For lift-off,the sacrificial layer 28 is now removed by plasma etching, gaseousetching or another process in the V-shaped areas between the μ-LEDs andbelow, so that the chips only rest with their layer 34 on thedelamination layer of the receiving elements.

FIG. 30 and FIG. 31 each show an example of a carrier structure 10 withexemplary 24 μ-LEDs 16 arranged in a matrix on a wafer (not shown). FIG.30 shows a total of 17 carrier elements 20. These are partly arranged ina mesa trench 38 between two adjacent μ-LEDs 16, partly also at thecorners of the respective μ-LEDs 16. This arrangement can lead to thefact that a total of fewer pick-up elements 20 are required than a totalnumber of μ-LEDs 16. In addition, a mounting element 20 in the exampleshown here can support or accommodate up to four adjacent μ-LEDs 16.

In FIG. 31, the base of receptacle 20 is not round as in FIG. 30, buthas a rectangular or square base. This means that the contact area 36,with which the mounting element is in contact with the μ-LED 16, mayvary. This can ensure stable mounting of the μ-LED 16, even if the μ-LED16 shifts slightly in its position in the x-direction or y-direction. Inother words, a total contact area consisting of all contact surfaces 36on the μ-LED 16 remains the same or at least approximately the same,even with small shifts in the lateral direction. Furthermore, themounting elements 20 can also be arranged on the outer edge of a carrierstructure 12 and engage on an outer lateral surface of a μ-LED 16. As anexample, it can be seen here that exactly three support points for thesame μ-LED can provide particularly stable spatial stabilization. Here,too, a mounting element 20 can support two or more adjacent μ-LEDs 16and thus reduce space requirements and thus costs through multiple use.In the examples shown, the contact area is shown much larger than thechip area. In practical implementations, the contact area issignificantly smaller to reduce the adhesive force so that thedelamination layer remains on the carrier and does not break off.

FIG. 32A shows an embodiment in which several μ-LEDs 16 have beenmonolithically produced on a carrier substrate. Each μ-LED has the shapeof a hexagon, i.e. 6 side faces, each facing a side face of an adjacentμ-LED. The corners of the individual μ-LEDs each rest on a mountingelement 20. In addition, an edge structuring has been carried out, i.e.trenches have been etched so that the μ-LEDs are only held by themounting elements. Each μ-LED comprises a centrally arranged and roundactive area 2 a. This is surrounded by an area 2 b, the diameter ofwhich substantially corresponds to the distance between two oppositeside surfaces of a μ-LED. In other words, the area extends to the sideedge of each hexagonal structure of the μ-LEDs, while the corners ofeach μ-LED do not include the area 2 b.

In a different embodiment, area 2 b is slightly larger, so that twoareas 2 b of two adjacent μ-LEDs would meet virtually extended beyondthe side edges. However, this part of the second area is removed duringprocessing of the deep edge structure. The second region now comprises alarger band gap generated by quantum well intermixing than the band gapof the active region 2 a. The quantum well intermixing was generated,for example, using one of the methods disclosed and presented in thisapplication. The quantum well intermixing and the resulting increase inthe band gap effectively keeps the charge carriers away from the edgeregions and thus the edges of the μ-LED, since there is an increaseddefect density there due to the processing, which leads to non-radiativerecombination.

FIG. 32B shows another version of the embodiment, which was created byan improved mask structuring. The benefit for this embodiment is toreduce the number of photomasks and transfer steps required. In thisversion, a photomask was chosen which leads to smaller bulges at thecorners. This results in this slightly changed structure.

In the examples shown here, the μ-LEDs are manufactured using varioussemiconductor technologies. The techniques disclosed in this applicationcan be used for this purpose. However, it is also possible to transferthe antenna structures in this way. The wafer onto which the transfer ismade can have contact areas, so that electrical contact is possible.Likewise, control, power sources and other elements may already bepresent in this wafer. The μ-LEDS transferred in this way will then befurther processed in several versions. For example, a converter layer ora light-shaping element will be applied to the μ-LED. In principle,individual μ-LEDs were transferred in these designs. However, theprocess is not limited to such. The above modules can also be formedwith these carrier structures to facilitate the transfer of suchmodules. The columns or the carrier elements are formed after it isknown what size the modules should have.

Traditionally, there are various ways of transferring chips from acarrier wafer to a corresponding target substrate.

State of the art transfer processes such as laser transfer printing or“self-assembly” of individual micro light emitting diode chips from asolution or electrostatically activated or diamagnetic transferprocesses are known.

An extension of these concepts achieved with the electrostatic transferis explained in more detail. A method is to be specified with whichoptoelectronic semiconductor chips with particularly small dimensions,i.e. μ-LEDs, are picked up and deposited and at the same time, thosewith a defect are sorted out.

FIG. 33A schematically shows a device 10 for picking up and placingoptoelectronic semiconductor chips as an example of an invention. Inthis example, the optoelectronic semiconductor chips are designed asμ-LEDs 11 and are arranged on a carrier 12 at a distance from eachother. The device 10 comprises a pick-up tool 13, an excitation element14 and a voltage source 15.

The excitation element 14 emits light 16 with which the μ-LEDs 11 areirradiated. The light 16 emitted by the excitation element 14 compriseswavelengths that generate electron-hole pairs in the optically activeregion of the μ-LEDs 11 by excitation. The electron-hole pairs cause anelectrostatic polarization within the μ-LEDs 11, which generates anelectric dipole field in the vicinity of the respective μ-LED 11. In thepresent embodiment, the pick-up tool 13 is arranged between theexcitation element 14 and the μ-LEDs 11. The pick-up tool 13 is at leastpartially transparent for the light 16 emitted by the excitation element14 so that the light 16 can reach the μ-LEDs 11.

The pick-up tool 13 has metal contacts embedded, for example, inpolydimethylsiloxane (PDMS for short) or another suitable material. Themetal contacts are connected to the voltage source 15. An electrostaticfield can be generated by applying a voltage to the metal contacts.Furthermore, the pick-up tool has 13 elevations 17, which extend from asurface on the underside of the pick-up tool 13 in the direction of theμ-LEDs 11.

Based on FIGS. 33A to 33D, a procedure for picking up and placing theμ-LEDs 11 with the aid of the fixture 10 is described below as anembodiment according to the proposed concept. The light 16 emitted bythe excitation element 14 causes an excitation and a resultingelectrostatic polarisation in the μ-LEDs 11. At the same time, thepick-up tool 13 is charged by the voltage source 15 in such a way thatan attractive interaction between the pick-up tool 13 and the μ-LEDs 11is caused.

The recording tool 13 is shut down to the μ-LEDs 11 until the elevations17 are in contact with the μ-LEDs 11 below. In this example, everysecond μ-LED 11 is in contact with one of the protrusions 17. As FIG.33B shows, the pickup tool 13 is then raised together with the LEDs 11adhering to the bumps 17. FIG. 33C shows an enlarged section of FIG.33B. FIG. 33C shows the electrostatic charge of pick-up tool 13 and thepolarization of the μ-LEDs 11. For simplicity, the excitation element 14and the voltage source 15 are not shown in FIG. 33B and all subsequentfigures.

The μ-LEDs 11 located between the elevations 13 are not lifted by therecording tool 13. Furthermore, μ-LEDs 11 are not lifted where the light16 emitted by the excitation element 14 causes little or no polarizationdue to defects in the μ-LEDs 11. These μ-LEDs 11 are highlighted in FIG.33A to 33 C. The lower polarization compared to intact μ-LEDs 11 makesit possible to sort out μ-LEDs 11 with corresponding defects withouthaving to test the μ-LEDs 11 beforehand. Then, as shown in FIG. 33D, theμ-LEDs 11 are transferred to a desired location using the recording tool13 and stored there.

FIG. 34 schematically shows a device 20 for picking up and placingoptoelectronic semiconductor chips as a further example of an invention.The device 20 shown in FIG. 34 is largely identical to the device 10 inFIG. 33A. The difference is that the excitation element 14 in FIG. 34 islocated below the carrier 12 on which the μ-LEDs 11 are located. In thiscase, the support 14 must be at least partially transparent to the light16 emitted by the excitation element 14 in order for photoluminescenceexcitation to occur in the μ-LEDs 11.

FIG. 35A schematically shows a cylindrical shaped pick-up tool 13, whichcan be designed like the drum of a laser printer. The pick-up tool 13 iselectrostatically charged in such a way that there is an attractiveinteraction between the surface of the pick-up tool 13 and the μ-LEDs 11below it due to the polarization caused by the photoluminescenceexcitation. As shown in FIG. 35B, the cylindrical pick-up tool 13 isrolled over the support 12 and those μ-LEDs 11 are picked up in whichsufficient polarization has been produced by the incident light 16.

FIG. 36 schematically shows a pick-up tool 13 with elevations 17 on itsunderside extending in the direction of the μ-LEDs 11 located below thepick-up tool 13. The light 16 emitted by the excitation element 14 notshown in FIG. 36 passes through the pick-up tool 13 onto the μ-LEDs 11.To allow the passage of the light 16, the pick-up tool 13 is made of amaterial that is at least partially transparent to the light 16.Alternatively, corresponding through-holes or light guides can beintegrated into the pick-up tool 13.

FIG. 37 shows the pick-up tool 13 from FIG. 36, but in FIG. 37, onlycertain μ-LEDs 11 are selectively irradiated with the light 16, e.g.every second μ-LED 11. To make this possible, correspondingthrough-holes or light guides may be integrated in the pick-up tool 13or a corresponding shadowing mask may be provided which allows the light16 to fall only on the specified μ-LEDs 11. As a result, only the μ-LEDs11 irradiated with the light 16 are excited to photoluminescence andonly these μ-LEDs 11 can be picked up by the pick-up tool 13, providedthat they form a sufficient polarization by the photoluminescenceexcitation.

FIG. 38 schematically shows a pick-up tool 13, which comprises acontinuous flat surface 21 on its underside. The flat surface 21 makesit possible to pick up μ-LEDs 11 arranged in different patterns and/orat different distances. Furthermore, shading elements, e.g. a mask, canbe provided to excite selectively only certain μ-LEDs 11 tophotoluminescence.

FIG. 39A to 39C shows the fixture 10 while placing the μ-LEDs 11. Afterpicking up the μ-LEDs 11 as shown in FIG. 33A to 33D, the pickup tool 13is transferred to a board shown in FIG. 39A on which some of the μ-LEDs11 are to be mounted.

Using the voltage source 15 shown in FIG. 39B, the electrostatic chargeof the pick-up tool 13 is changed in such a way that the attractiveinteraction between the pick-up tool 13 and the μ-LEDs 11 is reduced orconverted into a repulsive interaction. By means of the individuallycontrollable metal contacts in the pick-up tool, the electrical chargein certain areas of the pick-up tool can be changed in the desired wayso that only a predetermined number of μ-LEDs 11 are deposited on theboard 22. The pickup tool 13 is then removed from the board 22, as shownin FIG. 39C. The μ-LEDs 11 remaining on the pickup tool 13 can beremoved or placed elsewhere, for example on a cleaning tape.

FIGS. 40A through 40 C schematically illustrate various options forgenerating an electric field using pickup tool 13. The field lines 23shown in FIG. 40A through 40 C indicate the direction and strength ofthe electric field at the location.

In the configuration shown in FIG. 40A, charges are located in theelevations 17 of the pick-up tool 13, and the counter charges arelocated in the vicinity of the pick-up tool 13. This results in anelectric field around each of the bumps 17, similar to the field of apoint charge. In FIG. 40B, there are dipole charges in the pick-up tool13, arranged in such a way that the electric field strength isparticularly strong at the tips of the bumps 17. In FIG. 40C, the bumps17 of the pickup tool 13 are electrically charged and the counterchargesare arranged below the carrier 12 so that the μ-LEDs 11 to be picked upare located between the pick-up tool 13 and the countercharges and thuswithin the electric field.

The electric fields generated by the recording tool 13 should not behomogeneous in order to exert an effective force on the dipoles of theμ-LEDs 11 so that they can be recorded by the carrier 12. FIGS. 40A to40 C also show electric field lines 24 of μ-LEDs 11 generated by theexcitation. The interaction of the field lines 24 of the μ-LEDs 11 withthe field lines 23 of the pick-up tool 13 is not shown forsimplification.

FIGS. 41A and 41B show illustrations with regard to transfer steps of aconventional method and with regard to a method according to the conceptof a double transfer process. The parallel, error-free transfer of manyμ-LEDs from a carrier substrate 3 to a display substrate 7 plays adecisive role in the production of μ-displays. The number of necessarytransfer steps is important for the manufacturing costs. The fewertransfer steps required, the lower the corresponding process costs.Parallel to the cost consideration, the technical feasibility ofreducing the number of transfer steps is also relevant.

In general, the density of μ-LEDs on a carrier substrate is 3 orders ofmagnitude higher than on a μ-display. The ratio depends on the μ-LEDsize, the chip-to-chip distance (wafer pitch) on carrier substrate 3 andthe target resolution of the μ-display (pixel pitch).

The transfer from carrier substrate 3 to the target substrate 7 can becarried out according to a conventional method in such a way that theμ-LEDs are removed from carrier substrate 3 according to the pixel pitchof the display and transferred to the corresponding substrate 7. Thesize of the transfer stamp as well as the size of the removable area oncarrier substrate 3 and the total size of the μ-display then define thenumber of transfer steps for a μ-display. It is advantageous if thestamp size is selected in such a way that the display size can be fullypopulated by means of integer multiples of the stamp size in x and ydirection. In this way, individual transfer processes can be avoided.For the production of color displays, the transfer for all three colorsred, green, blue of the μ-LED onto the target substrate must be carriedout.

Both FIGS. 41A and 41B show a carrier substrate 3 on which μ-LEDs 1 havebeen formed. Accordingly, a carrier substrate 3 provides μ-LEDs of onecolor, for example red, green and blue. Now the number of transfer stepsby means of which μ-LEDs are transferred from a carrier substrate 3directly to a μ-display is to be determined, whereby this corresponds toa conventional method.

For example, the display has a spatial extension of 200 mm in thex-direction and 100 mm in the y-direction. The carrier substrate 3, forexample, has a diameter of 300 mm. The pitch between the μ-LEDs is 10μm. The pitch between the pixels of the display is 100 μm, ten times aslarge. A color display with red, green and blue μ-LEDs is to beproduced. Therefore, this whole process has to be done for each color.

FIG. 41A shows maximum stamp positions per carrier substrate 3 for asmall transfer stamp size. FIG. 41B shows maximum stamp positions percarrier substrate 3 for a relatively large transfer stamp size. In FIG.41A, the size of the transfer stamp is 10 mm in the x-direction and also10 mm in the y-direction. Accordingly, for a display area of 20,000 mm²(200 mm×100 mm) with the selected area of the transfer stamp of 100 mm²,a total of s=200 transfer steps must be performed for each color. Usingthe three colors red, green and blue results in 600 transfer steps forone display. FIG. 41A shows that up to 610 transfer steps can be carriedout with this design, allowing 86.3% of the wafer to be used. However,it should be noted that it is assumed that each transfer step does notinvolve a transfer error, i.e. all μ-LEDs to be transferred are alsopicked up.

Small transfer stamps result in a large area of use on the carriersubstrate 3 In other words, a large number of μ-LEDs can be removed froma carrier substrate if the transfer stamp is small. However, theresulting high utilization factor is associated with a large number oftransfer steps. FIG. 41B shows a design, in which the size of thetransfer die is designed with spatial extensions of 40 mm in anx-direction and 50 mm in a y-direction.

Accordingly, for a display area of 20,000 mm² with the selected area ofthe transfer stamp of 2,000 mm², a number of r=10 transfer steps must becarried out for each color. Using the three colors red, green and blueresults in only 30 transfer steps for one display. FIG. 41B shows,however, that up to 24 transfer steps can be carried out with thisdesign, which means that only 67.9% of the wafer can be used. As aresult, although larger transfer dies result in a smaller number oftransfer steps, the usable area on carrier substrate 3 is also smaller.In other words, a larger stamp cannot easily reach some areas on thecarrier substrate.

Now the number of transfer steps is to be determined by means of whichμ-LEDs are transferred from a carrier substrate 3 via an intermediatecarrier 5 to a target substrate for a μ-display. In contrast to theconventional method, instead of a display, an intermediate carrier 5 isnow first assembled in the same way as in the conventional method. Allsize specifications described above still apply. Accordingly, a transferstamp as shown in FIG. 41A requires s=200 transfer steps per color and atransfer stamp as shown in FIG. 41B requires r=10 transfer steps percolor.

Since the pitch of the μ-LED on the carrier substrate 3 is 10 μm, andthe pitch of the pixels of the display is ten times as large at 100 μm,the conventional transfer method can only transfer fewer μ-LEDs thanpossible by a factor of n=100. In other words, both stamps transfer lessμ-LED per transfer in the conventional manner than it would be possible.

In the method according to the proposed principle, all μ-LEDs present onthe carrier substrate 3 and accessible by the stamp are transferred tothe intermediate carrier 5 during the transfer. These are so-calledfirst transfer steps, which are carried out by means of a first transferstamp 4. In the proposed process, the intermediate carrier 5 is the samesize as the display, so that a display for one color can be completelyassembled with one transfer by means of a second transfer step using asecond transfer stamp 6 of the same size. Since the first density ofμ-LEDs on the intermediate carrier 5 is greater by a factor of n=100than the density of the pixels on the display, a number of n=100displays of one color is produced from an intermediate carrier 5. Forcolor displays, 3×100 second transfer steps are then required, which,together with the first transfer steps, result in a respective followingtotal number of transfer steps per 100 color displays:

For the small transfer stamp 4 as shown in FIG. 41A, this results in atotal number of 3×200+3∴100 transfer steps for 100 color displays, i.e.9 transfer steps per 1 color display. For the larger transfer stamp 4 asshown in FIG. 41B, the total number of transfer steps is 3×10+3×100 for100 color displays, i.e. 3.3 transfer steps per 1 color display.

This is a significant improvement over the conventional method, whichrequires 600 transfer steps per 1 color display for the small transferstamp shown in FIG. 41A and 30 transfer steps per 1 color display forthe larger transfer stamp shown in FIG. 41B. The transfer steps percolor display are average values from which real manufacturing processesmay differ within tolerances and due to defects.

FIG. 42 shows a first embodiment of an inventive start structure for aninventive process in a top view. This start structure is used to executethe two transfer steps safely and reliably. FIG. 42 shows μ-LEDs 1arranged at module areas 11, which adhere to a carrier substrate 3 bymeans of first anchor elements 9. The module areas 11 can be assembledfrom one or several carrier substrates 3.

The first anchor elements 9 are connected to the carrier substrate 3 andare designed to hold several module areas 11 detachably between thefirst anchor elements 9 in such a way that the module areas 11 can beseparated from the carrier substrate 3 in first transfer steps S 2 witha first defined minimum lifting force transverse to the substrate planeby means of the first transfer stamp 4, moved out and then transferredto the intermediate carrier 5. The minimum lift-off force must beapplied at least to enable lift-off and must be set in a defined mannerby the anchor elements 9.

The adhesive force with which the μ-LEDs 1 adhere to the first transferstamp 4 is greater than the first defined minimum lifting force. FIG. 43shows the first embodiment according to FIG. 42 of the startingstructure in an enlarged view using the proposed concept for theprocedure.

The enlarged view shows that the μ-LEDs 1 adhere to module areas 11 bymeans of second anchor elements 13. The module areas 11 thus carry aplurality of transferable μ-LEDs. In particular, second anchor elements13 are formed which are connected to the module areas 11 and areconfigured to hold μ-LEDs 1 detachably between the second anchorelements 13 in such a way that the μ-LEDs 1 are separated from anintermediate carrier 5 by means of the second transfer stamp 6 in arespective second transfer step S3 with a second defined minimum liftingforce transverse to the plane of a respective module area 11, moved outand then transferred to the target substrate 7.

The adhesive force with which the μ-LEDs 1 adhere to the second transferstamp 6 is greater than the second defined minimum lifting force. FIG.42 and FIG. 43 show the first starting structures that can be used tocarry out the presented method. By means of first anchor elements 9 arespective first transfer step can be performed and by means of secondanchor elements 13 a respective second transfer step can be performedsafely and reliably. By means of the anchor structures 9, 13 definedminimum lift-off forces are set for a lift-off during the two transfersteps.

FIG. 44 shows a further illustration with regard to the production of afirst launch structure in accordance with the invention. On the left, around carrier substrate 3 is shown, in which rectangular module areas 11are drawn. Carrier substrate 3 has the double anchor elements in theform of the first anchor elements 9 for the module areas 11 and thesecond anchor elements 13 for the micro light emitting diodes. On theright side, an enlarged representation of a rectangular module area 11is shown. The module also includes lifting elements 15 at two diagonallyopposite corners. These serve to ensure that the module areas 11 can besafely transferred. The lifting elements 15 can alternatively be formedin the four corners of a module area 11 or in the four corners of amodule area 11 and additionally in its center. Lifting elements 15provide working surfaces for a first transfer stamp for lifting moduleareas 11. Thus, module areas with μ-LEDs 1 can be assembled fromdifferent carrier substrates 3.

In some aspects, the lifting elements 15 are designed as μ-LEDs 1, whichare not to be transferred and are directly attached to the module areas11. Lifting elements 15 are thus μ-LEDs 1, which are directly connectedto module areas 11 without second anchor elements 13. Without anchorelements, the lifting elements 15 have a high adhesive force on therespective wafer area 11. Lifting elements 15 create a square or roundsurface or structures such as crosses. The number of lifting elements 15can be selected proportionally to the size of the module area 11. If thelifting elements 15 are only structures directly connected to modulearea 11, the arrangement of the structure of the lifting elements 15 isselected as an integer multiple of the display pixel pitch to generatethe least loss of chip area. If μ-LEDs 1 are provided as liftingelements 15, they can no longer be used as display elements.

Alternatively or cumulatively, according to the lifting elements 15positioning elements 17 can be designed as positioning aids for aspatially accurate transfer. Lifting elements 15 are then thepositioning elements 17. The accuracy of a wafer pitch of the individualμ-LEDs on the transferred module areas 11 is not affected by thetransfer process. Since the positioning accuracy of large-area moduleareas 11 in relation to one another is not negatively influenced by theexpansion effects of a transfer stamp during the transfer, greateroverall accuracy can also be achieved when “denominating” a temporaryintermediate carrier 5. This also results in lower tolerances in thefinal assembly of displays with micro light emitting diodes.

FIG. 45 shows an example of an inventive method. In a first step, anintermediate carrier 5 is produced in the target size of the displayproduct with the same μ-LED density as the carrier substrate 3. Thebasic shape of the intermediate carrier 5 is rectangular. It is thenthinned out during transfer to the display. For this purpose, theintermediate carrier 5 is provided on which module areas 11 of wafer 3can be temporarily transferred completely. In a second stamping step ortransfer step S3, individual μ-LEDs with the correct pixel pitch areremoved again to be transferred to a final target substrate 7. Animportant criterion is the positional accuracy during transfer to theintermediate carrier 5 as well as the spatially accurate, preferablyerror-free placement during transfer to the target substrate 7.

To create a color display, the following steps are carried out for eachof the colors red, green and blue, in particular in the example of FIG.46:

With a first step S1, μ-LEDs 1 are generated on a carrier substrate 3with a first density. In this process, first anchor elements 9 andsecond anchor elements 13 are formed on the carrier substrate 3 forpositioning module areas 11 and μ-LEDs 1. These anchor elements 9, 13thus provide double anchor element structures or double anchor elementstructures as starting structures for the process. After the carriersubstrate 3 has been processed, the module areas 11 located on thecarrier substrate 3 are tested in such a way that, for example,functioning μ-LEDs are distinguished from defective μ-LEDs 1, a yield isdetermined or color locations are determined.

With a second step S2, a respective first transfer step is carried outby a first transfer stamp 4, which transfers the μ-LEDs 1 to anintermediate carrier 5 with the first density. Depending on the testresults, only certain module areas 11 are arranged on an intermediatecarrier 5. In this way, for example, only functioning module areas 11 oronly module areas 11 with suitable color can be formed.

Depending on the design, a multiple transfer takes place until theintermediate carrier 5 is completely equipped with module areas 11.These are attached to the intermediate carrier 5 with an adhesivematerial or adhesive film. The adhesive force can be generated byself-hardening or cross-linking by means of ultraviolet light orexposure to high temperature. Optionally, thermal or thermocompressivetreatment of the intermediate carrier 5 can be carried out, whichimproves the planarity and/or adhesion. An intermediate carrier 5 isused for each color, for example a 12.3 inch intermediate carrier 5. Theintermediate carrier 5 can be equipped with module areas 11 of differentcarrier substrates 3.

With a third step S3 a respective second transfer step is executed.Here, a second transfer stamp 6 is used to transfer the μ-LEDs 1 fromthe intermediate carrier 5 to a target substrate 7 with a second densitythat is a factor n smaller than the first density. The distance betweenthe pixels and thus also between the μ-LEDs on the target substrate 7corresponds to a multiple of the distance between μ-LEDs of the sametype on the intermediate carrier 5 and can be different in both spatialdirections. In other words, μ-LEDs on the intermediate carrier areselected and transmitted based on the pitch on the target substrate 7.This result in a thinning of the μ-LEDs on subcarrier 5, but acorresponding number of color displays can be created from threeassembled subcarriers.

The target substrate 7 provides a common array area for each of the narrays, especially for all three colors. Size and shape of theintermediate substrate 5 and the second transfer stamp 6 are equal toeach other and preferably equal to the array surface. In this way, abackplane of a display can be equipped with μ-LEDs of one color in asecond transfer step. If intermediate carrier 5 and second transferstamp 6 are smaller than the display by a factor k, correspondingly ksecond transfer steps must be carried out, which increases themanufacturing effort. The target substrate 7 can be equipped withseveral intermediate carriers 5, for example to produce colored screens.

The display can be further processed by means of a further processingS4. For example, the production of a respective electrical top contactin the case of vertical micro light emitting diodes or the production ofboth electrical contacts in the case of horizontal micro light emittingdiodes. In addition, optical out-coupling structures or out-couplinglayers or surface refinement layers can be formed, which can serve toimprove the black impression, for example. A modulation can also becarried out.

FIG. 46 shows the first embodiment of a start structure for the proposedmethod in cross-section. The start structure comprises several μ-LEDs 1,which are connected to module areas 11 by means of second anchorelements 13. These in turn are connected to a carrier substrate 3 byfirst anchor elements 9. Between carrier substrate 3 and module areas 11on the one hand and μ-LEDs 1 and module areas 11 on the other hand,anchor elements 9, 13 are configured in such a way that with a definedfirst minimum lifting force of the lifting first transfer stamp 4, themodule areas 11 are separated from the module areas 11 in a firsttransfer step S2 and with a defined second minimum lifting force of thelifting second transfer stamp 6, the μ-LEDs 1 are separated from themodule areas 11, lifted and then transferred in a second transfer stepS3.

FIGS. 47A to 47E show a further example of a proposed method using thefirst start structure shown.

FIG. 47A shows how a large number of module areas 11 with μ-LEDs 1 aredetached from the first anchor elements 9 and the wafer 3 with a stepS2.1. This is done by means of a first transfer stamp 4. For lifting offthe module areas 11, the adhesive force of the μ-LEDs 1 on the moduleareas 11 (second adhesive force) is greater than the adhesive force(first adhesive force) of the module areas 11 on the carrier substrate3. In addition, the adhesive force of the first transfer stamp 4 on theμ-LEDs 1 is also greater than the first adhesive force of the moduleareas 11 on the carrier substrate 3. The first minimum lifting forceapplied by the first transfer stamp 4 is again greater than the firstadhesive force of the module areas 11 on the carrier substrate 3 andsmaller than the second adhesive force of the μ-LEDs 1 on the moduleareas 11 and less than the adhesive force of the μ-LEDs 1 on the firsttransfer stamp 4.

For successful placement of the module areas 11 carrying μ-LEDs 1 on theintermediate support 5 as described in FIG. 47B, the second adhesiveforce of the μ-LEDs 1 on the module areas 11 must be greater than theadhesive force of the μ-LEDs 1 on the first transfer stamp 4. Theadhesive force of the module areas 11 on the intermediate support 5 mustbe greater than the adhesive force of the μ-LEDs 1 on the first transferstamp 4. First anchor elements 9 and second anchor elements 13 are usedto set the respective first and second adhesive forces. Thus, the firstadhesive force between the module areas 11 and the wafer 3 is providedby the first anchor elements 9. The respective second adhesive forcebetween the μ-LEDs 1 and the module areas 11 is provided by the secondanchor elements 13. The release force applied by the first transferstamp 4 must be greater than the adhesive force of the μ-LEDs 1 on thefirst transfer stamp 4 and smaller than the second adhesive force of theμ-LEDs 1 on the module areas 11. The release force is the minimum forcethat must be applied in order to carry out releasing.

FIG. 47B shows a subsequent step S2.2 of applying the module areas 11carrying μ-LEDs 1 to the intermediate carrier 5, which is also carriedout using the first transfer stamp 4.

By selecting a suitable material, a connection between the module areas11 and the intermediate support 5 can be provided with the requiredadhesive force. For example, an adhesive can be used. The adhesive forceof the μ-LEDs 1 on the first transfer stamp 4 can also be changed bysuitable movement guidance of the first transfer stamp 4 during liftingand setting down, e.g. by movement guidance with shear component, i.e.parallel to the plane of the intermediate carrier. The adhesive force ofthe μ-LEDs 1 on the first transfer stamp 4 can be reduced, e.g. duringsetting down.

Steps S2.1 and S2.2 are carried out several times until, for example,for a color of red, green or blue, the intermediate carrier 5 is fullyloaded.

FIG. 47C shows a subsequent step S3.1 of lifting the μ-LEDs 1 from themodule areas 11 for transfer to the target substrate 7, which is done bya second transfer stamp 6. The μ-LEDs 1 are released from the secondanchor elements 13 and the intermediate carriers 5. Here μ-LEDs 1 arereleased simultaneously from several intermediate carriers. The densityof the μ-LEDs 1 on the module areas 11 does not correspond to thedensity of the μ-LEDs 1 on the target substrate 7. For example, thefirst density can be twice as high as the second density. Accordingly,the second stamp has 6 sensing elements 19, which correspond to thedistance of the μ-LEDs 1 on the target substrate 7. FIG. 47C shows thatthe first density of μ-LEDs 1 on module areas 11 is twice as high as thesecond density of μ-LEDs 1 on target substrate 7.

The adhesion of the second transfer stamp 6 must also be stronger thanthe adhesion of the μ-LEDs 1 on the intermediate carrier 5. To lift offthe μ-LEDs 1, the adhesive force of the μ-LEDs 1 on the second transferstamp 6 must be greater than the second adhesive force of the μ-LEDs 1on the module areas 11. Furthermore, the adhesive force of the moduleareas 11 on the intermediate carrier 5 must also be greater than thesecond adhesive force of the μ-LEDs 1 on the module areas 11. Thedefined second minimum lifting force applied by the second transferstamp 6 must be greater than the second adhesive force of the μ-LEDs 1on the module areas 11 and less than the adhesive force of the moduleareas 11 on the intermediate carrier 5 and less than the adhesive forceof the μ-LEDs 1 on the second transfer stamp 6.

For successful placement of the μ-LEDs 1 from the second transfer stamp6 onto the target substrate 7 as described in FIG. 47D, the adhesiveforce of the μ-LEDs 1 on the target substrate 7 must be greater than theadhesive force of the μ-LEDs 1 on the second transfer stamp 6.Conversely, the release force applied by the second transfer stamp 6 isgreater than the adhesive force of the μ-LEDs 1 on the second transferstamp 6 but less than the adhesive force of the μ-LEDs 1 on the targetsubstrate 7. The second anchor elements 13 as well as connecting meansand the movement guide of the second transfer stamp 6 are used to setthe respective adhesive forces. The respective second adhesive forcebetween the μ-LEDs 1 and the module areas 11 is provided by the secondanchor elements 13.

FIG. 47D shows a subsequent step S3.2 of applying the μ-LEDs 1 to thetarget substrate 7, which is also done with the second transfer stamp 6.μ-LEDs 1 are applied to a target substrate 7, which is part of adisplay.

The adhesive force of the μ-LEDs 1 on the second transfer stamp 6 canalso be changed by suitable movement guidance of the second transferstamp 6 during lifting and setting down, e.g. by movement guidance withshear component, i.e. parallel to the target substrate plane. Theadhesive force of the μ-LEDs 1 on the second transfer stamp 6 can bereduced, e.g. during setting down. By selecting a suitable material, aconnection between the μ-LEDs 1 and the target substrate 7 can beprovided with the required adhesive force. For example, adhesives,intervias or solder can be used.

Steps S3.1 and S3.2 are carried out several times until, for example,target substrate 7 of a display is fully populated for all colors ofred, green and blue.

FIG. 47E shows further processing steps S4 on the target substrate 7,including the production of mechanical and electrical contacts on thetarget substrate 7 by means of conventional processes, such asdeposition of an Intervia material, curing and subsequent structuringand/or back etching.

For example, a respective electrical top contact is produced in verticalμ-LEDs or both electrical contacts are produced in horizontal μ-LEDs. Inaddition, out-coupling structures or outcoupling layers or surfacerefinement layers are formed, for example to improve the blackimpression. Modularization can also be carried out. In this way, a largenumber of arrays A in μ-display design can be produced simply andcost-effectively.

FIG. 48 shows a further example of a connection of μ-LEDs 1 at moduleareas 11, for which additional anchor elements 13 and second releaseelements 23 are provided in addition to the second anchor elements 13and on these. Before executing a second transfer step S3 the μ-LEDs 1are in contact with second anchor elements 13 and second enablingelements 23, each of which is connected to a module area 11. The μ-LEDs1 are mechanically connected to the module area 11 with a large adhesiveforce by means of the second anchor elements 13 and the second enablingelements 23.

FIG. 49 shows the embodiment according to FIG. 48, whereby the secondrelease elements 23 have been removed, thus effectively and purposefullyreducing the adhesive force of the μ-LEDs 1 to the module area 11.

FIG. 50 shows a second start structure with μ-LEDs 1, which areconnected to module areas 11 by means of second anchor elements 13 andsecond release elements 23, which are connected to a wafer 3 by means offirst anchor elements 9 and first release elements 21. The μ-LEDs 1 arein contact with second anchor elements 13 and second enabling structures23, which in turn are in contact with module area 11. The module areas11 are in contact with first anchor elements 9 and first enablingelements 21. In contrast to the first start structure according to FIG.46, enabling elements 21, 23 are used in addition to anchor elements 9,13. In this way adhesive forces can be reduced in a targeted manner sothat module areas 11 are removed first and μ-LEDs 1 afterwards byremoving first release elements 21 and then second release elements 23.

The first anchor elements 9 for module areas 11 can vary in number, sizeand distribution. For example, they can be used to optimize a releaseprocess depending on the size of the module areas 11 in such a way thatadhesive forces are selected in the correct ratio to lifting forces. Aminimum lift-off force must be applied to enable lift-off. This minimumlift-off force can be set in a defined manner using anchor elements andrelease elements.

FIGS. 51A to 51E show a further example of an inventive method using thesecond launch structure shown in FIG. 50, which uses first releaseelements 21 and second release elements 23 in addition to first anchorelements 9 and second anchor elements 13. FIG. 51B shows that the firstrelease elements 21 are removed first. FIG. 51C shows that in a firsttransfer step S2 module areas 11 are detached from wafer 3 and placed onthe intermediate carrier 5. Then, as shown in FIG. 51D, the secondrelease elements 23 are removed. In a second transfer step S3, theμ-LEDs 1 of module areas 11 are detached and placed on the targetsubstrate 7. This step can be seen in FIG. 51E.

FIG. 52A and 52B illustrate the aspect of selectivity of enablingelements. In FIG. 52A, the first share elements 21 are removed. FIG. 52Bshows how two second release elements 23 are removed after the firstrelease element 21 has been removed, the module areas 11 containingμ-LEDs 1 have been transferred to an intermediate carrier 5 andprotective layers 25 have been removed.

Selectivity between first enabling elements 21 and second enablingelements 23 for successive removal can be achieved in different ways:

a) Different materials with different properties can be used, which arematched to each other. For example, SiO₂ can be etched with HF. Si canalso be etched with SF 6. Further possible materials are for exampleSiO₂, Si, Al₂O₃, SiN, SiON, AlN, HfOx, metallic layers as well asorganic materials, which can be used as adhesives.

b) Different rates of material removal can be used. For example, byexposing relatively large areas of the first release element 21 to theremoval process. In second release approval element 23, relatively smallareas are exposed to the removal process. For example, only smallopenings are designed in such a way that liquids and/or gases can onlypenetrate slowly.

c) The second release elements 23 can be protected from the removalprocess by protective layers 25. After removal of the first releaseelements 21, the protective layers 25 can be removed, for example by drychemical, wet chemical or gaseous etching, after which the secondrelease elements 23 can be removed.

d) The release elements 21, 23 can be removed in different ways. Forexample, by means of chemical processes such as wet chemitry or by meansof gas phases, by means of thermal processes, by means of mechanicalprocesses, by means of optical processes, for example by using UV light.

FIGS. 53A to 53F show embodiments of the arrangement of second anchorelements 13 and second release elements 23 between μ-LEDs 1 and moduleareas 11, which are here alternatively designed as a complete carriersubstrate 3. The second anchor elements 13 for the μ-LEDs 1 can vary innumber, size and distribution. For example, a release process can thusbe optimized depending on the size of the μ-LEDs 1 in such a way thatadhesive forces are selected in the correct ratio to lift-off forces.The second release elements 23 rest against the second anchor elements13 accordingly. Anchor element 13 and release element 23 are alsoarranged on a module area 11, which is a carrier substrate 3. The mainsurface area of the module area 11 is greater than or equal to the mainsurface area of the release element 23.

FIG. 53A shows an embodiment in which a second anchor element 13 forms asmaller main surface area to μ-LED 1 and is partially connected to μ-LED1 in an edge area at one corner of μ-LED 1. A second release element 23comprises a larger main surface area than the μ-LED 1 and is arranged onthe μ-LED 1 in such a way that the second release element 23 at leastpartially frames the second anchor element 13.

FIG. 53B shows a further embodiment in which two second anchor elements13 each form a smaller main surface compared to μ-LED 1 and are arrangedin the edge area at opposite corners of the μ-LEDs 1. A second releaseelement 23 comprises a larger main surface area compared to the μ-LEDand is arranged on the μ-LED 1 in such a way that the second releaseelement 23 at least partially frames the second anchor elements 13. FIG.53C shows a further embodiment in which a second anchor element 13 formsa smaller main surface compared to the μ-LED 1 and is arrangedcompletely on the μ-LED 1 in a core area of the μ-LED 1. A secondrelease element 23 completely frames the second anchor element 13.

FIG. 53D finally shows another embodiment in which a plurality of μ-LEDs1 are arranged in a row to each other. Two second anchor elements 13each form a smaller main surface compared to a μ-LED 1 and are eachpartially arranged in the edge area at opposite corners of a μ-LED 1.Each anchor element 13 is arranged on two μ-LEDs 1 arranged side by sideand comprises a surface area uncovered by μ-LEDs 1. A second releaseelement 23 comprises a larger main surface area than all μ-LEDs 1 and isarranged on the μ-LEDs 1 in such a way that the second release element23 completely frames the second anchor elements 13.

FIG. 53E shows a further embodiment in which twelve second anchorelements 13 together form a smaller main surface than the μ-LED 1 andare arranged in the interior of the μ-LEDs 1 in the form of a matrix. Asecond release element 23 comprises a larger main surface area than theμ-LED 1 and completely frames the second anchor elements 13. Anchorelements 13 and release element 23 are also arranged on a module area11, which can alternatively be a wafer 3. The main surface area of themodule area 11 is greater than or equal to the main surface area of therelease element 23.

FIG. 53F shows a final embodiment in which a second anchor element 13forms a larger main surface area compared to μ-LED 1 and in its corearea a protrusion which is completely arranged at μ-LED 1. A secondrelease element 23 comprises a larger main surface area than the μ-LED 1and is arranged on the μ-LED 1 in such a way that the second releaseelement 23 completely frames the elevation of the second anchor element13 and is arranged on the second anchor element 13. The main surface ofthe module area 11 is greater than or equal to the main surface of thesecond anchor element 13. The main surface of the release element 23corresponds to the main surface of the second anchor element 13.

In the following, various devices and arrangements as well as methodsfor manufacturing, processing and operating as items are again listed asan example. The following items present different aspects andimplementations of the proposed principles and concepts, which can becombined in various ways. Such combinations are not limited to thoselisted below:

342. Pixel with several μ-LEDs for generating a pixel of a display,where

the pixel is formed from at least two subpixels, in particular twosubpixels of the same color emission, and in particular each subpixel isformed by a μ-LED;

wherein a subpixel separating element is provided between two adjacentsubpixels of the same pixel element; and

wherein the subpixel separating element is configured to be separatingwith respect to electrical control of the respective subpixels and isconfigured to be optically coupling with respect to the light emitted bythe respective subpixels.

343. Pixel according to item 342, wherein the subpixels have a commonepitaxial layer and the subpixel separating element extends trench-likeinto the epitaxial layer transversely to an epitaxial layer plane in amain emission direction.

344. Pixel according to any of the preceding items, wherein thesubpixels of the pixel are independently electrically contactable and/orcontrollable.

345. Pixel according to any of the preceding items, in which the atleast two sub-pixels have a common active layer separated by thesub-pixel separator.

346. Pixel according to any of the preceding items, in which thesubpixel separator extends to or at least partially through an activelayer of the pixel.

347. Pixel according to any of the preceding items, in which thesubpixel separation element is formed by quantum well intermixinggenerated by a diffused dopant, in particular in the region of theactive layer.

348. Pixel according to any of the preceding items, in which alight-shaping structure is formed having first and second regions, theregions extending at least partially into a semiconductor material ofthe pixel.

349. Pixel according to item 348, wherein the light-shaping structureextends into a partial area of the active layer.

350. Pixel according to any of the preceding items, in which thelight-shaping structure has a converter material in second areas.

351. Pixel according to any of the preceding items with a light-shapingor photonic structure having features according to any of the followingor preceding items.

352. Pixel according to any of the preceding items, further comprising amicrolens extending over the surface of a pixel.

353. Pixel according to any of the preceding items, in which atransparent conductive layer is formed on a surface.

354. Pixel according to any of the preceding items, wherein at least onecontact surface for contacting at least one subpixel is provided on aside opposite to the light emission side.

355. Display with a large number of pixels according to any of thepreceding items,

wherein a pixel element separation layer is provided between twoadjacent pixels, which is adapted to separate electrically the adjacentpixels with respect to the controlling of the respective pixels and toseparate optically the adjacent pixels with respect to the light emittedby the pixels.

356. Display according to item 355, wherein the pixels and theassociated sub-pixels have a common epitaxial layer and the pixelelement separation layer extends trench-like into the epitaxial layertransversely to the epitaxial layer plane in the main emissiondirection.

357. Display according to any of the preceding items, wherein a trenchdepth d1 of the pixel element separation layer is greater than a trenchdepth of the sub-pixel separation element.

358. Display according to any of the preceding items, in which adjacentpixels or sub-pixels comprise an active layer separated by a pixelelement separation layer and/or a sub-pixel separation element.

359. Display according to any of the preceding items, further comprisinga support layer having contact areas corresponding to contact areas ofpixels, wherein in the support layer at least one of the followingelements is provided:

-   -   electrically conductive lines to a power supply of the pixel,    -   Current driver circuits or supply circuits, in particular        according to any of the items 836 to 930;    -   Control circuit for adjusting a brightness;    -   one or more fuses that are electrically connected to at least        one subpixel of a pixel.

360. Method for calibrating a pixel, comprising the steps of:

-   -   driving a subpixel of a pixel according to any of the item 836        to 930;    -   acquiring of defect information of a subpixel;    -   storing of the defect information in a memory unit of the        control unit.

361. Method according to item 360, wherein the driving, acquisition andstorage is performed sequentially for all individual subpixels of apixel.

362. Array with at least two μ-LEDs, wherein a respective μ-LED betweenan n-doped layer and a p-doped layer forms an active zone suitable forlight emission, characterized in that between two adjacent formed μ-LEDsmaterial of the layer sequence from the n-doped side and from thep-doped side up to or in cladding layers or up to or at least partiallyinto the active zone is interrupted or removed in such a way thatmaterial transitions with a maximum thickness dC are formed, wherebyelectrical and/or optical conductivities in the material transition arereduced.

363. Array according to any of the preceding items, characterized inthat, at the material transition, the active zone and, at least on oneside of the active zone, a residual layer of small thickness.

364. Array according to item 362 or 363, characterized in that theremoved material is at least partially replaced by a filling material.

365. Array according to any of the preceding item, characterized in that

the removed material is at least partially replaced by a materialcomprising a relatively small band gap and thus absorbing light of theactive zone.

366. Array according to any of the preceding items, characterized inthat

the removed material is at least partially replaced by a material withan increased refractive index, in particular greater than the refractiveindex of the doped material or a filler material.

367. Array according to any of the preceding items, characterized inthat

the light absorbing material and/or the material with increasedrefractive index has been applied to a respective material transition.

368. Array according to any of the preceding items, characterised inthat the material has been formed with an increased refractive index bydiffusing or implanting a refractive index-increasing material into thefilling material, in particular into a respective cladding layer.

369. Array according to any of the preceding items, characterised inthat

a material for increasing light absorption and/or a material forincreasing electrical resistance has been diffused or implanted into theactive zone of a respective material transition.

370. Array according to any of the preceding items, characterised inthat

along the material transitions, at or in these, at least one opticalstructure, in particular a photonic crystal and/or a Bragg mirror, isgenerated.

371. Array according to any of the preceding items, characterised inthat

an electrical bias voltage is applied to the two main surfaces of thematerial transitions by means of two opposite electrical contacts and anelectrical field is generated by a respective material transition.

372. Array according to any of the preceding items, characterised inthat by means of an n-doped material and/or p-doped material applied orgrown on at least one of the two main surfaces of the materialtransitions, an electric field is generated by a respective materialtransition.

373. Array according to any of the preceding items, characterised inthat the exposed main surfaces of the material transitions and/orexposed surface regions of the μ-LED are electrically insulated andpassivated by means of a respective passivation layer, in particularcomprising silicon dioxide.

374. Array according to any of the preceding items, characterised inthat

the main surfaces of the μ-LED by contact layers are electricallycontacted.

375. Array according to any of the preceding items, characterised inthat

the material and/or the material transitions between one μ-LED and itsadjacent μ-LEDs are formed differently from one another, in particulardepending on the direction.

376. Array according to any of the preceding items, further comprising alight-shaping structure which is applied to a surface of the arrayfacing the main emission direction, which in particular has a photonicstructure with features according to any one of the following orprevious items.

377. Array according to any of the preceding items, in which thelight-shaping structure has areas of different refractive index.

378. Array according to item 376, in which the light-shaping structureextends into the semiconductor material of the μ-LED.

379. Array according to any of items 376 to 378, in which portions ofthe light-shaping structure are filled with a converter material.

380. Array according to any of the preceding items, further comprising aconverter material applied to a surface facing the main radiationdirection.

381. Method for producing an array of optoelectronic pixels, inparticular a micropixel emitter array or a micropixel detector array,comprising the steps:

providing a whole-surface layer sequence of an n-doped layer and ap-doped layer along the array, between which an active zone suitable forlight emission is formed;

-   -   at least partially removing of material between adjacent pixels        to be formed from the n-doped side and from the p-doped side so        that a material transition with a maximum thickness dC remains,        which comprises the active zone, such that the electrical and/or        optical conductivities between adjacent pixels are reduced.

382. Method according to item 381, wherein the step of removing materialcomprises removing the layer sequence from the n-doped side and from thep-doped side up to or into undoped cladding layers or up to or at leastpartially into the active zone.

383. Method according to item 381, characterized in that from then-doped side and/or from the p-doped side the removed material is atleast partially replaced by a filler material.

384. Method according to any of the preceding items, characterised inthat

the removed material is at least partially replaced from the n-dopedside and/or from the p-doped side by a material having a relativelysmall band gap and thus absorbing light of the active zone.

385. Method according to any of the preceding items, characterised inthat

the removed material is replaced from the n-doped side and/or from thep-doped side by a material with an increased refractive index, inparticular greater than the refractive index of the doped material or afiller material.

386. Method according to any of the preceding items, characterised inthat

the light absorbing material and/or the material with increasedrefractive index is applied to a respective material transition.

387. Method according to any of the preceding items, characterised inthat

the material with increased refractive index is formed by diffusing orimplanting a material increasing the refractive index into the fillingmaterial, in particular into a respective cladding layer.

388. Method according to any of the preceding items, characterised inthat

a material for increasing light absorption and/or a material forincreasing electrical resistance is diffused or implanted into theactive zone from the n-doped side and/or from the p-doped side.

389. Method according to any of the preceding items, characterised inthat

at least one optical structure, in particular a photonic crystal and/ora Bragg mirror, is generated from the n-doped side and/or from thep-doped side along the material transitions, at or in these.

390. Method according to any of the preceding items, characterized inthat

two electrical contacts opposite each other are formed from the n-dopedside and from the p-doped side for applying an electrical bias voltageto the two main surfaces of the material transitions and for generatingan electric field through a respective material transition.

391. Method according to any of the preceding items, characterised inthat

by means of an n-doped material and/or p-doped material applied or grownon at least one of the two main surfaces of the material transitions, anelectric field is established through a respective material transition.

392. Method according to any of the preceding items, characterised by

electrically insulating and passivating the exposed main surfaces of thematerial transitions and/or exposed surface areas of the pixels by meansof a respective passivation layer, in particular comprising silicondioxide.

393. Method according to any of the preceding items, characterised by

electrical contacting of the main surfaces of the pixels by means ofcontact layers.

394. Method according to any of the preceding items, characterised inthat

the material and/or the material transitions between a pixel and itsneighbouring pixels are formed differently from one another, inparticular depending on the direction.

395. Method according to any of the preceding items, characterised inthat

the steps are first performed for one major surface of the array andthen, after a substrate change, for the other major surface of thearray.

396. Carrier structure with flat optoelectronic components, especiallyμ-LEDs, comprising

-   -   a flat carrier substrate, and    -   at least two receiving elements that are designed to hold a        first μ-LED detachably between the at least two receiving        elements in such a way that the μ-LED can be moved out with a        defined minimum force perpendicular to a carrier structural        plane; wherein at least one receiving element of the at least        two receiving elements is designed to simultaneously hold and/or        support a second, adjacently arranged μ-LED.

397. Carrier structure according to item 396, wherein the receivingelements are arranged on the support substrate in such a way that theμ-LED is held by three receiving elements.

398. Carrier structure according to item 396, wherein at least tworeceiving elements of the three receiving elements are configured tohold and/or support a further adjacent μ-LED.

399. Carrier structure according to one of the items 396 to 398, whereina delamination layer is provided, which is arranged between thereceiving element and the μ-LED and remains on the receiving element inparticular after the μ-LED has been moved out.

400. Carrier structure according to any of the preceding items, whereinthe receiving elements are arranged in a mesa trench of a semiconductorwafer.

401. Carrier structure according to any of the preceding items, in whichthe support substrate and the receiving elements are made in one piece.

402. Carrier structure according to any of the preceding items, whereinthe support elements are configured to hold a μ-LED laterally and from abottom side of the μ-LED.

403. Carrier structure according to any of the preceding items, whereinthe receptacle elements have μ-LED holding surfaces which are inclinedrelative to the carrier substrate plane so that a holding force on theμ-LED is reduced when the μ-LED is moved away from the receptacleelements.

404. Carrier structure according to any of the preceding items, whereinat least one of the receiving elements is adapted to receive a lateralcorner portion or side surface of a μ-LED.

405. Carrier structure according to any of the preceding items, whereina contact area between the receiving element and μ-LED is less than1/20, in particular less than 1/50 of a total area of the μ-LED.

406. Carrier structure according to any of the preceding items, in whichthe first μ-LED and second μ-LED partially rest on the at least onereceiving element, and between the first and second μ-LED a part of thesurface of the receiving element is exposed or rises between the firstand second μ-LED.

407. μ-LED with a semiconductor layer stack which comprises an activelayer and which is arranged on a carrier structure according to any ofthe preceding items.

408. μ-LED according to item 407, said μ-LED comprising a peripheralregion formed by the mesa trench, wherein the active layer in saidperipheral region has a band gap increased by quantum well intermixing.

409. μ-LED according to any of the preceding items, in which an edgeregion comprises a protuberance, which is arranged on the supportstructure.

410. Carrier structure according to any of the preceding items articlescontaining a μ-LED, in particular a μ-LED according to any of thepreceding items.

411. Method for transferring at least two μ-LEDs, in particularoptoelectronic components, wherein the at least two μ-LEDs are arrangedon a common receiving element of a carrier and the carrier comprises asacrificial layer on which the μ-LEDs are arranged, comprising thesteps:

-   -   removing of the sacrificial layer on which the μ-LEDs are        arranged, so that the μ-LEDs are held by the common receiving        element;    -   removing at least one of the at least two μ-LEDs from the common        mounting element.

412. Method for producing a μ-LED, comprising the steps:

-   -   providing of a substrate;    -   applying of a sacrificial layer, in particular comprising AlGaAs        or InGaAlP, to the substrate;    -   creating a functional layer stack with an active layer between        oppositely doped semiconductor layers;    -   applying of a first electrically conductive contact layer on a        first major surface side of the functional layer stack;    -   forming at least one holding structure which is attached to the        substrate, supports the functional layer stack and from which a        contacted functional layer stack can be broken off during        lift-off;    -   at least partial removing of the sacrificial layer located        between a second major surface side of the functional layer        stack and the substrate;    -   applying a second electrically conductive contact layer to the        second main surface side of the functional layer stack in the        area of the removed sacrificial layer.

413. Method according to item 412, wherein the step of generating afunctional layer stack comprises the step of forming one or more quantumwells or quantum wells in the active layer.

414. Method according to any of the preceding items, wherein the step ofcreating a functional layer stack comprises the step of:

-   -   forming of a quantum well intermixing in edge regions of the        active layer and/or in regions, which are at least adjacent to        the retaining structure or adjacent to a possible break-off        edge.

415. Method according to item 414, wherein the step of forming a quantumwell intermixing comprises:

-   -   providing a structured photomask on the functional layer stack;    -   applying of a dopant with first process parameters;    -   diffusing and/or formation of quantum well intermixing with        second process parameters.

416. Method according to any of the preceding items, in which the stepof creating a functional layer stack comprises the step forming aquantum well intermixing with features according to any of the precedingitems.

417. Method one of the previous articles, further comprising: liftingthe contacted functional layer stack by breaking it off the holdingstructure and positioning it on a secondary substrate.

418. Method according to any of the preceding items, in which the stepof forming the support structure comprises

-   -   forming of the retaining structure, in particular having a        conical shape, on the functional layer stack from its first main        surface side into the substrate.

419. Method according to any of the preceding items, in which the stepof applying a first electrically conductive contact layer comprises:

-   -   Application of a first bearing layer to the functional layer        stack on its first main surface side;    -   applying of the first electrically conductive contact layer to        the first support layer, wherein the first support layer and the        first electrically conductive contact layer are attached to the        substrate at least at one point and thus form the support        structure at least partially.

420. Method according to any of the preceding items, wherein the stepcomprises applying a second electrically conductive contact layer:

-   -   applying a second support layer to the second major surface side        of the functional layer stack facing the substrate directly to        the functional layer stack; and    -   applying the second electrically conductive contact layer to the        second base layer.

421. Method according to any of the preceding items, in which thestructure is formed at least partially epitaxially or by means of steamor electroplating.

422. Method according to any of the preceding items, in which thestructure of the functional layer stack is passivated by means of theretaining structure, whereby the retaining structure can in particularbe transparent.

423. Method according to any of the preceding items, characterised by

-   -   removing of the sacrificial layer by wet chemical etching.

424. Method according to any of the preceding items, characterised by

-   -   removing of the sacrificial layer in two steps, before and after        applying the second electrically conductive contact layer.

425. Method according to any of the preceding items, further comprising:

covering one flank of the functional layer stack with a passivationlayer.

426. Method according to any of the preceding items, characterised by

-   -   diffusing of a metal, in particular Zn, from a flank of the        functional layer stack into an outer edge region of the        functional layer stack.

427. Method according to any of the preceding items, characterised by

applying of the first and/or the second electrically conductive contactlayer by sputtering, vaporizing or electroplating.

428. μ-LED or μ-LED module or array of μ-LEDs, comprising:

-   -   a functional layer stack; wherein    -   a first electrically conductive contact layer is applied to a        first main surface side of the functional layer stack facing        away from a substrate and a second electrically conductive        contact layer is applied to a second main surface side of the        functional layer stack facing the substrate; wherein    -   the contacted functional layer stack is supported by at least        one holding structure which is attached to the substrate and        from which the contacted functional layer stack can be broken        off during lift-off.

429. μ-LED or μ-LED module or array of μ-LEDs according to item 428,characterized in that

the functional layer stack has an optically active layer betweenoppositely doped layers, in particular an active layer formed by one ormore quantum wells.

430. μ-LED or μ-LED module or array of μ-LEDs according to any of thepreceding items, in which the active layer has an increased band gap inedge regions of the μ-LED and/or in regions, which are at least adjacentto the holding structure or adjacent to a possible break-off edge.

431. μ-LED or μ-LED module or array of μ-LEDs according to any of thepreceding items, comprising quantum well intermixing in edge regions ofthe active layer or in regions of the active layer adjacent to thesupport structure or adjacent to a possible break-off edge.

432. μ-LED or μ-LED module or array of μ-LEDs according to any of thepreceding items, characterized in that

the contacted functional layer stack was transferred to a secondarysubstrate by lifting and positioning.

433. μ-LED or μ-LED module or array of μ-LEDs according to any of thepreceding items characterized in that the substrate comprises GaAs.

434. μ-LED or μ-LED module or array of μ-LEDs according to any of thepreceding items, characterised in that

the support structure comprises in particular InGaAlP or AlGaAs or BCBor an oxide, for example SiO₂, or a nitride or a combination of suchmaterials, and/or is in particular electrically non-conductive.

435. μ-LED or μ-LED module or array of μ-LEDs according to any of thepreceding items, characterised in that

a first supporting layer comprises, in particular InGaAlP and/or AlGaAs,attached to the functional layer stack on the first main surface side.

436. μ-LED or μ-LED module or array of μ-LEDs according to any of thepreceding items, characterised in that

a second supporting layer attached to the functional layer stack on thesecond main surface side comprises in particular InGaAlP and/or AlGaAs.

437. μ-LED or μ-LED module or array of μ-LEDs according to any of thepreceding items, characterised in that

the first and/or the second electrically conductive contact layercomprises ITO or ZnO or a metal and/or in particular are attached to afirst and a second supporting layer.

438. μ-LED or μ-LED module or array of μ-LEDs according to any of thepreceding items, characterised in that

the μ-LED is smaller than 70 μm, in particular smaller than 50 μm orsmaller than 20 μm or smaller than 10 μm.

439. Method for picking up and placing optoelectronic semiconductorchips, wherein

electron-hole pairs are generated in optoelectronic semiconductor chipsand an electric dipole field is thereby generated in the vicinity of therespective optoelectronic semiconductor chip,

a recording tool generates an electric field, and the optoelectronicsemiconductor chips are picked up with the pick-up tool during or afterthe generation of the electron-hole pairs and deposited at predeterminedpositions.

440. Method according to item 439, where the optoelectronicsemiconductor chips are μ-LEDs or LEDs.

441. Method according to item 439 or 440, wherein the optoelectronicsemiconductor chips for generating the electron-hole pairs areirradiated with light having a predetermined wavelength or apredetermined wavelength range.

442. Method according to item 441, wherein the light for generating theelectron-hole pairs is incident on the optoelectronic semiconductorchips through the pick-up tool.

443. Method according to item 442, wherein the optoelectronicsemiconductor chips are arranged on a carrier and the light forgenerating the electron-hole pairs falls through the carrier onto theoptoelectronic semiconductor chips.

444. Method according to any of the preceding items, wherein a pluralityof optoelectronic semiconductor chips are provided and the electricaldipole fields are generated only in selected optoelectronicsemiconductor chips of the plurality of optoelectronic semiconductorchips.

445. Method according to any of the preceding items, whereby the pick-uptool generates an electric field only in predetermined areas.

446. Method according to any of the preceding items, wherein the pick-uptool has a plurality of elevations on a surface facing theoptoelectronic semiconductor chips, and the optoelectronic semiconductorchips are picked up by the elevations of the pick-up tool.

447. Method according to any of the preceding items, wherein at least aportion of a surface of the pick-up tool facing the optoelectronicsemiconductor chips is flat, and the optoelectronic semiconductor chipsare picked up with the flat portion of the pick-up tool.

448. Method according to any of the preceding items, wherein the pick-uptool has the shape of a cylinder, which is rolled over theoptoelectronic semiconductor chips to pick up the optoelectronicsemiconductor chips.

449. Method according to any of the preceding items, wherein fordepositing the optoelectronic semiconductor chips the electric fieldgenerated by the pick-up tool is changed.

450. Method according to any of the preceding items, wherein the pick-uptool for picking up the optoelectronic semiconductor chips directlycontacts the optoelectronic semiconductor chips and holds them by meansof Van der Waals forces.

451. Apparatus for picking up and putting down optoelectronicsemiconductor chips, μ-LED arrays or μ-LED according to any of thepreceding or subsequent items, comprising:

an excitation element for generating electron-hole pairs inoptoelectronic semiconductor chips in order to generate an electricdipole field in the vicinity of the respective optoelectronicsemiconductor chip, and

a pick-up tool for picking up and depositing the optoelectronicsemiconductor chips, wherein the pick-up tool is configured such that itgenerates an electric field, then picks up the optoelectronicsemiconductor chips with the electron-hole pairs generated by theexcitation element and deposits the optoelectronic semiconductor chipsat predetermined locations.

452. Apparatus according to item 451, wherein the excitation element isconfigured to generate light with a predetermined wavelength or apredetermined wavelength range for generating the electron-hole pairs inthe optoelectronic semiconductor chips.

453. Apparatus according to item 452, wherein the excitation element isarranged in such a way that the light for generating the electron-holepairs is incident on the optoelectronic semiconductor chips through thepick-up tool or through a carrier on which the optoelectronicsemiconductor chips are arranged.

454. Apparatus according to one of the items 451 to 453, wherein thepick-up tool has a plurality of projections on a surface facing theoptoelectronic semiconductor chips, and the optoelectronic semiconductorchips are picked up by the projections of the pick-up tool.

455. Apparatus according to any one of the items 451 to 453, wherein atleast a portion of a surface of the pick-up tool facing theoptoelectronic semiconductor chips is flat and the optoelectronicsemiconductor chips are picked up with the flat portion of the pick-uptool.

456. Apparatus according to any one of the items 451 to 453, wherein thepick-up tool has the shape of a cylinder, which is rolled over theoptoelectronic semiconductor, chips to pick up the optoelectronicsemiconductor chips.

457. Method for processing a number of arrays of optoelectroniccomponents, in particular μ-LEDs or μ-LED arrangements, comprising thefollowing steps:

-   -   generating of μ-LEDs on a carrier substrate with a first        density;    -   executing of first transfer steps by means of a first transfer        stamp, which transfers the optoelectronic microchips onto an        intermediate carrier of the first density;    -   carrying out second transfer steps by means of a second transfer        stamp, which transfers the optoelectronic microchips from the        intermediate carrier to a target substrate with a second density        smaller by a factor n than the first density, which provides a        common array area for a respective one of the number of arrays,        in particular for all three colors, wherein the size of the        intermediate carrier is equal to or larger than that of the        second transfer stamp and the size of the second transfer stamp        is equal to or smaller by a factor k than that of the array        area.

458. Method according to item 457, characterized in that the μ-LEDs aregenerated connected to respective module areas, which are generatedconnected to the carrier substrate.

459. Method according to item 458, characterized in that when the μ-LEDsare generated, first armature elements for connecting with a firstadhesive force are formed between module areas and the carrier substrateand/or second armature elements for connecting with a second adhesiveforce are formed between the μ-LEDs and the module areas.

460. Method according to any of the preceding items, characterised inthat

-   -   when carrying out the first transfer steps, the lifting force of        the lifting first transfer stamp is set to be greater than the        first adhesive force and less than the second adhesive force in        such a way that the module areas are lifted off the carrier        substrate and transferred to the intermediate carrier.

461. Method according to any of the preceding items, characterised inthat

-   -   when carrying out the second transfer steps, the lifting force        of the lifting second transfer stamp is set to be greater than        the second holding force in such a way that the μ-LEDs are        lifted off the module areas and transferred to the target        substrate.

462. Method according to any of the preceding items, characterised inthat

when generating the μ-LEDs, first release elements for connecting withan additional first adhesive force are additionally formed between themodule areas and the carrier substrate and/or second release elementsfor connecting with an additional second adhesive force are additionallyformed between the μ-LEDs and the module areas.

463. Method according to item 462, characterized in that when carryingout the first transfer steps, the lifting force of the lifting firsttransfer stamp is set to be greater than the total first adhesive forceand less than the total second adhesive force in such a way that themodule areas are lifted off the wafer and transferred to theintermediate carrier.

464. Method according to item 463, characterized in that the additionalinitial holding force has been reduced, especially to zero, by removingthe first release elements beforehand.

465. Method according to any of the preceding items, characterised inthat

when carrying out the second transfer steps, the lifting force of thelifting second transfer stamp is set to be greater than the total secondholding force in such a way that the μ-LEDs are lifted off the moduleareas and transferred to the target substrate.

466. Method according to item 465, characterized in that the additionalsecond holding force has been reduced, in particular to zero, by meansof prior removing the second release elements.

467. Method according to any of the preceding items, characterized inthat

for the adhesion of the module areas on the intermediate carrier,materials with a respective adhesive force greater than the total secondadhesive force must be used.

468. Method according to any of the preceding items, characterized inthat

when generating the μ-LEDs for carrying out the first transfer steps,lifting elements are formed directly on the module areas for lifting andtransferring the module areas to the intermediate carrier.

469. Method according to any of the preceding items, characterised inthat

when generating the microchips for carrying out the first transfersteps, positioning elements are formed directly on the module areas forthe precise transfer of the module areas to the intermediate carrier.

470. Method according to any of the preceding items, characterised inthat

to carry out the second transfer steps, tapping elements are formed onthe second transfer die for thinning the microchips to the seconddensity.

471. Method according to any of the preceding items, characterised inthat

the size of the, in particular rectangular, first transfer stamp ischosen to be smaller by a factor s than the size of the, in particularround, wafer in such a way that the size of an area of lost μ-LEDs atthe edge of the carrier substrate for the first transfer for completeloading of the intermediate carrier is small, in particular per colorless than or equal to 20% or less than or equal to 30% of the carriersubstrate area.

472. Method according to any of the preceding items, characterised inthat

the size of the, in particular rectangular, first transfer stamp ischosen to be smaller than the size of the intermediate carrier by thefactor r in such a way that the number of first transfer steps r for thefirst transfer for complete loading of the intermediate carrier issmall, in particular per color less than or equal to 10 or less than orequal to 50.

473. Method according to any of the preceding items, characterised inthat

the shape of the intermediate carrier corresponds to the shape of thesecond transfer stamp and said shape in particular to the shape of thearray surface.

474. Method according to any of the previous items, characterised inthat

the intermediate carrier is equipped with tested module areas of thecarrier substrate or several, in particular different, carriersubstrates.

475. Method according to any of the preceding items, characterised inthat

the distances between the μ-LEDs on the respective carrier substratecorrespond to the distances between the μ-LEDs on the intermediatecarrier substrate.

476. Method according to any of the preceding items, characterised inthat

the distances between microchip on a respective intermediate carrier andon a respective target substrate in an x-direction are different fromthose in a y-direction.

477. Method according to any of the preceding items, characterised inthat

the target substrate is loaded with several intermediate carriers.

478. Method according to any of the preceding items, characterised inthat

the color of the μ-LEDs of a respective intermediate carrier ismonochrome red, green or blue and the number of arrays is formed fromthree intermediate carriers, which have μ-LEDs of different colors toeach other.

479. Method according to any of the preceding items, characterised inthat

between carrier substrate and module areas first release elements andthen between μ-LEDs and module areas second release elements areselectively removed.

480. Array with a multitude of μ-LEDs, μ-LED modules or μ-LED arrays,which are manufactured in particular for each of the colors red, greenand blue by the following steps:

-   -   generating μ-LEDs, on a carrier substrate with a first density;    -   executing of first transfer steps by means of a first transfer        stamp, which transfers the μ-LEDs to an intermediate carrier of        the first density;    -   carrying out second transfer steps by means of a second transfer        stamp which transfers the μ-LEDs from the intermediate carrier        to a target substrate with a second density which is smaller by        a factor n than the first density, wherein the intermediate        carrier provides a common array area for a respective one of the        arrays, in particular for all three colors, wherein the size of        the intermediate carrier is equal to or larger than that of the        second transfer stamp and the size of the second transfer stamp        is equal to or smaller by a factor k than that of the array        area.

481. Array comprising a plurality of μ-LEDs, μ-LED modules or μ-LEDarrays manufactured by a process according to any of the precedingitems.

482. Start structure for use in a process according to any of thepreceding items, characterized in that

module areas are attached to a carrier substrate by means of firstanchor elements, and

μ-LEDs are attached to the module areas by means of second armatureelements.

483. Start structure for use in a process according to any of thepreceding items,

characterised in that

module areas are fixed to a carrier substrate by means of first anchorelements and removable first release elements, and

μ-LEDs are attached to the module areas by means of second armatureelements and removable second release elements.

484. Method for producing modules of μ-LEDs, comprising the steps of:

-   -   generating at least one layer stack providing a base module on a        carrier having a first layer, an active layer applied thereto        and a second layer formed thereon;    -   exposing a surface area of the first layer facing away from the        substrate;    -   forming a first contact on a surface area of the second layer        facing away from the carrier;    -   forming a second contact on the surface area of the first layer        facing away from the carrier.

485. Method according to item 484, characterized in that forming asecond contact comprises:

-   -   forming an electrically insulating dielectric over a portion of        the active layer and the second layer    -   forming the second contact with a conductive material, which        electrically contacts the remote surface area of the first layer        via the dielectric to a surface area of the second layer remote        from the carrier.

486. Method according to item 484 or 485, characterised by exposing thesurface region of the first layer remote from the substrate by means ofa flat edge structuring of the at least one stack of layers, inparticular from the side of the second layer, a flat trench inparticular being produced around the respective stack of layers.

487. Method according to any of the preceding items, characterised by

generating a plurality of base modules as a matrix along an X-Y planealong at least one row and along at least one column, wherein basemodules of a respective row are oriented in the same way.

488. Method according to item 487, characterized in that the basemodules of two adjacent lines are oriented in the same way; or that

the base modules of two adjacent lines are oriented in oppositedirections, whereby contacts of the same polarity, in particular firstcontacts, are thus arranged adjacent to one another.

489. Method according to item 488, characterised by

generating of a common layer stack of two adjacent base modules orientedopposite to each other.

490. Method according to any of the preceding items, characterised by atleast one of the following steps:

-   -   grouping a number of base modules to form at least one μ-LED        module, in particular rectangular or square along the X-Y plane,        wherein, in particular in a plurality of rows, each row has the        same columns occupied by base modules; and    -   forming the at least one μ-LED module from the plurality of base        modules by means of a deep edge structuring through the first        layer, in particular from the side of the second layer.

491. Method according to any of the preceding items, characterised inthat

the base modules are arranged on a different carrier when structuringthe deep edges, as opposed to exposing the first and second contacts.

492. Method according to any of the preceding items, characterised by atleast one of the following steps:

-   -   detaching the base module or μ-LED module from the carrier Laser        Lift-Off; and    -   detaching the base module or μ-LED module from the carrier,        using a mechanical process.

493. Method according to any of the preceding items, characterised by a

contacting the contacts of the μ-LED module to a replacement carrier orend carrier, especially by means of flip-chip technology.

494. Method according to item 493, characterized in that common contactareas can be created for contacts of adjacent oppositely oriented basemodules of the μ-LED module.

495. Method according to any of the preceding items, characterized inthat

the first layer is n-doped and the second layer is p-doped, the activelayer being configured in particular to emit blue or green light; and/orin that

the first layer is p-doped and the second layer is n-doped, the activelayer being configured in particular to emit red light.

496. Method according to any of the preceding items, characterized inthat

the at least one layer stack is created by epitaxy; and/or in that

exposure and/or grouping is performed by means of etching.

497. Method according to any of the preceding items, further comprisinga

generating of quantum well intermixing in areas of the active layeradjacent to a deep edge structuring.

498. μ-LED module comprising at least one layer stack forming a basemodule, with a first layer formed on a carrier, an active layer and asecond layer, wherein a first contact is formed in or on a surfaceregion of the second layer facing away from the carrier, and a secondcontact is formed in or on the surface region of the first layer facingaway from the carrier, and the first and second contact are spaced apartfrom one another.

499. μ-LED module according to item 498, in which a light-emittingsurface is formed on a side of the stack of layers facing away from thefirst and second contact.

500. μ-LED module according to item 498, characterized in that thesecond contact is formed by means of a dielectric to the transitionlayer and to the second layer electrically insulated from and on thesurface region of the second layer remote from the carrier.

501. μ-LED module according to item 499, characterized in that the μ-LEDmodule comprises a plurality of base modules arranged in a matrix of atleast one row and at least one column.

502. μ-LED module according to item 501, in which a μ-LED adjacent tothe μ-LED module is separated by a deep edge structuring.

503. μ-LED module according to item 502, in which regions of the activelayer which run adjacent to a deep edge structure have an elevated bandstructure produced in particular by quantum well intermixing.

504. μ-LED module according to any of the preceding items, characterizedin that

the base modules of two adjacent lines are oriented in oppositedirections so that contacts of the same polarity, in particular firstcontacts, are arranged adjacent to each other.

505. μ-LED module according to any of the preceding items, characterisedin that

the module, in particular a light-emitting diode module, has beenproduced by means of a process according to any of the preceding items.

506. μ-display or μ-LED display module with

-   -   an all-surface target matrix formed on a first carrier, which        has rows and columns of μ-LEDs, occupy-able locations,    -   one or more μ-LED modules following one of the items 498 to 505        comprising one or more base modules whose size corresponds to        the vacant positions;    -   characterised in that    -   the μ-LED modules are positioned and electrically connected to        the first carrier in the target matrix in such a way that a        number of base modules remain unoccupied in the target matrix,        at least some of which each have at least one sensor element        positioned and electrically connected.

507. μ-display or μ-LED display module according to item 506,characterized in that

a plurality of full-surface target matrices formed on the first carrierand of equal or different size to one another are formed along rows andcolumns with target matrix-occupy-able locations at respective distancesfrom one another.

508. μ-display or μ-LED display module according to item 506 or 507,characterized in that

the base modules form rectangles in a matrix plane, and in μ-LED modulesany number of base modules adjacent to each other along a common sideare grouped together.

509. μ-display or μ-LED display module according to any of the precedingitems, characterized in that

at least one μ-LED module comprises four base modules in two rows andtwo columns.

510. μ-display or μ-LED display module according to any of the precedingitems, characterized in that

at least one μ-LED module comprises three base modules in two rows andtwo columns.

511. μ-display or μ-LED display module according to any of the precedingitems, characterized in that

at least seven μ-LED modules, each with four base modules, and

at least two μ-LED modules, each with three base modules, are positionedand electrically connected to the target matrix .

512. μ-display or μ-LED display module according to item 511,characterized in that

in that at least two positions which are unoccupied by base modules areproduced, at which in each case at least one sensor element ispositioned and electrically connected.

513. μ-display or μ-LED display module according to item 512,characterized in that

the positions occupied by sensor elements are framed by base modules.

514. μ-display or μ-LED display module according to any of the precedingitems, characterized in that

the base modules are configured to emit electromagnetic radiation from afirst side of the first carrier.

515. μ-display or μ-LED display module according to any of the precedingitems, characterized in that

the μ-LED modules comprise base modules, which are configured assubpixels.

516. μ-display or μ-LED display module according to any of the precedingitems, characterized in that

the locations of the target matrices are configured as subpixels of apixel.

517. μ-display or μ-LED display module according to any of the precedingitems, characterized in that

a plurality of sensor elements are formed as part of sensor means formedon said first carrier to receive electromagnetic radiation incident on afirst side of said first carrier.

518. μ-display or μ-LED display module according to any of the precedingitems, characterized in that

at least one sensor element is configured as a vital sign monitoringsensor.

519. μ-display or μ-LED display module according to item 519, where

said vital sign monitoring sensor is disposed within a display screen orbehind the rear surface of a display screen, and said vital signmonitoring sensor is adapted to measure one or more vital signparameters of a user placing a body part to the front major surface ofthe display screen at said vital sign monitoring sensor.

520. μ-display or μ-LED display module according to any of the precedingitems, characterized in that

a base module comprises in each case a first layer, which is formed on asecond carrier and on which an active transition layer is formed and onwhich a second layer is formed, a first contact being connected to asurface region of the second layer which faces away from the secondsupport, a second contact being connected to a surface region of thefirst layer which faces away from the second support.

521. μ-display or μ-LED display module according to item 520, in which

the second contact is formed by means of a dielectric to the transitionlayer and to the second layer, electrically insulated from and on thesurface region of the second layer remote from the second carrier.

522. μ-display or μ-LED display module according to any of the precedingitems, characterized in that

the respective sensor element is adapted in the form of a μ-photodiode,or in the form of a phototransistor, or in the form of a photoconductor,or in the form of an ambient light sensor, or in the form of an infraredsensor, or in the form of an ultraviolet sensor, or in the form of aproximity sensor, or in the form of an infrared component.

523. Method for producing a μ-display or μ-LED display module with awhole-surface target matrix formed on a first carrier and having rowsand columns of target matrixes which can be occupied by base modules,

wherein a number of base modules are formed on a second carrier in astarting matrix having a spacing, equal to the target matrix, of pointswhich can be occupied by base modules, in particular by means of a flatmesa etching, are grouped there, in particular by means of a deep mesaetching, to form a number of μ-LED modules and these μ-LED modules areseparated from the second carrier, in particular by means of laserlift-off or a mechanical or chemical process,

characterised in that

the μ-LED modules are positioned and electrically connected on the firstcarrier in the target matrix in such a way that a number of base modulesremain unoccupied in the target matrix, at least some of which at leastone sensor element in each case is positioned and electricallyconnected.

524. Method according to item 523, characterized in that a plurality offull-surface target matrices of identical or different sizes formed onthe first carrier are formed along rows and columns with targetmatrix-occupy-able locations at respective distances from one another.

525. Method according to any of the preceding items, characterised inthat

the base modules form rectangles in a matrix plane, and in μ-LED modulesany number of base modules adjacent to each other along a common sidecan be grouped together.

526. Method according to any of the preceding items, wherein in at leastone μ-LED module four base modules can be grouped in two rows and twocolumns.

527. Method according to any of the preceding items, wherein in at leastone μ-LED module three base modules can be grouped in two rows and twocolumns.

528. Method according to any of the preceding items, characterised inthat

at least seven μ-LED modules, each with four base modules, and at leasttwo μ-LED modules, each with three base modules, are positioned andelectrically connected to the target matrix in such a way that at leasttwo positions which are unoccupied by base modules are generated atwhich in each case at least one sensor element is positioned andelectrically connected.

529. Method according to any of the preceding items, wherein thepositions occupied by sensor elements are framed by base modules.

530. Method according to any of the preceding items, wherein the basemodules are configured to emit electromagnetic radiation from a firstside of the first carrier.

531. Method according to any of the preceding items, characterised inthat

a plurality of sensor elements are formed as part of sensor means formedon said first carrier to receive electromagnetic radiation incident on afirst side of said first carrier.

532. Method according to any of the preceding items, characterised inthat

a sensor element is configured as a vital sign monitoring sensor.

533. Method according to item 532, characterised in that

said vital sign monitoring sensor is disposed within a display screen orbehind the rear surface of a display screen, wherein said vital signmonitoring sensor is adapted to measure one or more vital signparameters of a user who places a body part to the front major surfaceof the display screen at said vital sign monitoring sensor.

534. Method according to any of the preceding items, characterised inthat

a base module has in each case a first layer formed on a second carrier,on which an active transition layer and on said active transition layera second layer is formed, a first contact being connected to a surfaceregion of the second layer facing away from the support, a secondcontact being connected to a surface region of the first layer facingaway from the second support.

535. Method according to item 534, characterized in that the secondcontact is formed by means of a dielectric to the transition layer andto the second layer, electrically insulated from and on the surfaceregion of the second layer remote from the second carrier.

536. Method according to any of the preceding items, characterised inthat

a sensor element is formed in each case in the form of amicro-photodiode, or in the form of a phototransistor, or in the form ofa photo-resistor, or in the form of an ambient light sensor, or in theform of an infrared sensor, or in the form of an ultraviolet sensor, orin the form of a proximity sensor, or in the form of an infraredcomponent.

537. μ-LED module comprising:

-   -   a body with a first major surface and four lateral surfaces;    -   at least three contact pads arranged on the first main surface,        wherein a μ-LED with an edge length of 15 μm or less is arranged        on at least one of the at least three contact pads;    -   a plurality of contact bars, one contact bar being electrically        connected to one of the at least three contact pads in each        case, and the three contact bars being arranged on the first        main surface and at least one of the four side surfaces.

538. μ-LED module according to item 537, further comprising: a fourthcontact bar arranged on a second of the four side faces and which

-   -   is connected on the first major surface to a fourth contact pad        electrically connected to the at least one μ-LED; or    -   is electrically connected on the first main surface to an        optically transparent contact pad which electrically connects        the at least one μ-LED on a side opposite the at least one of        the three contact pads.

539. μ-LED module according to item 537, in which the second sidesurface of the four side surfaces has only the fourth contact bar.

540. μ-LED module according to any of the preceding items, where atleast two of the three contact bars are arranged on different sidesurfaces.

541. μ-LED module according to any of the preceding items, in which thebody forms a prismatic body in which the first major surface forms anangle of 90° or more with each of the four lateral surfaces.

542. μ-LED module according to any of the preceding items, furthercomprising:

-   -   second major surface substantially opposite the first major        surface; wherein

the second main surface has a larger area than the area of the firstmain surface.

543. μ-LED module according to any of the preceding items, where theside surfaces are not perpendicular to the first main surface.

544. μ-LED module according to any of the preceding items, furthercomprising:

-   -   a second main surface opposite the first main surface;    -   at least three contact pads arranged on the second main surface        and connected to one of the at least three contact bars on at        least one of the four side surfaces.

545. μ-LED module according to any of the preceding items, in which thecontact bars and/or the contact pads comprise a metal tab, in particulara vapour-deposited metal tab, the thickness of which is less than 5 μm,in particular less than 2 μm.

546. μ-LED module according to any of the preceding items, the bodycomprising

-   -   at least one through hole at least partially filled with an        electrically conductive material, wherein the electrically        conductive material on the first main surface is connected to        one of the at least three contact pads arranged on the first        main surface.

547. μ-LED module according to any of the preceding items, in which thebody comprises a recess on the second main surface in which at least onecontact bar runs, which connects a contact pad on the second mainsurface to a through-hole and at least one optoelectronic componentarranged on the first main surface is connected to the through-hole.

548. μ-LED module according to any of the preceding items, in which thebody comprises silicon and/or has a thickness of less than 30 μm, inparticular in the range 5 to 15 μm.

549. μ-LED module according to any of the preceding items, in which thecontact bars each run along one corner of two side surfaces from thefirst main surface to the second main surface.

550. Method for producing μ-LED module, comprising the steps:

-   -   providing a structured membrane wafer having a plurality of        substantially V-shaped trench-shaped depressions such that a        first major surface of the structured membrane wafer bounded by        trenches forms an angle of 90° or greater with the edges of the        trenches;    -   producing of contact pads on the first main surface of the        membrane wafer, including optional rewiring    -   applying of at least one μ-LED;    -   applying of a temporary support facing the first main surface;    -   Etching back the membrane wafer to around or just before the        trenches;    -   applying of rear contacts and optional separation to form a        μ-LED module.

551. Method for producing a pixel array comprising the steps of:

-   -   providing a substrate for the field-like arrangement of pixels        on the substrate and for electrical contacting of the pixels,        said substrate providing a set of primary contacts for a pixel,        said set of primary contacts being for electrically contacting a        group of μ-LEDs of said pixel, said substrate also providing a        set of spare contacts for said pixel,    -   equipping the primary contacts of the pixel with the group of        μ-LEDs, whereby the set of replacement contacts of the pixel is        not equipped,    -   identifying a faulty μ-LED or a faulty contact in the group of        μ-LEDs, and    -   equipping one spare contact of the set of spare contacts of the        pixel with a spare μ-LED for the faulty μ-LED or the faulty        contacting.

552. Method according to item 551, characterized in that the steps ofidentifying a defective μ-LED in the group of μ-LEDs and providing areplacement contact with a replacement μ-LED for the identified μ-LEDare repeated until a replacement μ-LED is present in the pixel for eachμ-LED identified as defective.

553. Method according to any of the preceding items, characterised inthat

a μ-LED identified as faulty is not removed.

554. Method according to any of the preceding items, characterised inthat

a μ-LED identified as defective and the replacement μ-LED are intendedto emit light of the same color.

555. Method according to any of the preceding items, characterised inthat

the group of μ-LEDs comprises one or more sets of RGB μ-LEDs.

556. Method according to any of the preceding items, characterised inthat

no replacement contact of the pixel is equipped with a replacementμ-LED, if no faulty μ-LED is found in the pixel.

557. Method according to any of the preceding items, characterised inthat

the primary contacts and/or the replacement contacts are configured forcontacting the μ-LED or the replacement μ-LEDs on the anode side or onthe cathode side or both on the anode and cathode side.

558. Method according to any of the preceding items, characterised inthat

a μ-LED or a replacement μ-LED is a μ-LED or a μ-LED module or a basemodule according to features according to any of the preceding items.

559. Method according to any of the preceding items, characterised inthat

an electrical contact for an identified, faulty μ-LED is disconnected.

560. Method according to any of the preceding items, characterised inthat

the replacement contact is equipped with a replacement μ-LED for a μ-LEDidentified as faulty, irrespective of the color of the light emitted bythe replacement μ-LED.

561. Method according to any of the preceding items, characterised inthat

all primary contacts of the pixel are equipped with μ-LEDs.

562. Pixel field, with:

a substrate for field-like arrangement of pixels on the substrate andfor electrical contacting of the pixels,

the substrate providing a set of primary contacts for at least onepixel, the set of primary contacts of the pixel being adapted forelectrical contacting of a group of μ-LEDs, the substrate also providinga set of spare contacts for the at least one pixel,

wherein the primary contacts of the pixel are equipped with the group ofμ-LEDs,

wherein the group of μ-LEDs comprises a faulty, deactivated μ-LED, and

wherein one spare contact of said set of spare contacts of said pixel isequipped with a spare μ-LED as a replacement for said faulty,deactivated μ-LED.

563. Pixel field according to item 562, characterised in that

the number of occupied spare contacts is different for at least twopixels.

564. μ-display comprising a pixel array according to any of thepreceding items or a pixel array produced by a process according to anyof the preceding items.

The description with the help of the exemplary embodiments does notlimit the various embodiments shown in the examples to these. Rather,the disclosure depicts several aspects, which can be combined with eachother and also with each other. Aspects that relate to processes, forexample, can thus also be combined with aspects where light extractionis the main focus. This is also made clear by the various objects shownabove.

The invention thus comprises any features and also any combination offeatures, including in particular any combination of features in thesubject-matter and claims, even if that feature or combination is notexplicitly specified in the exemplary embodiments.

1. A μ-LED comprising: a functional layer stack having an active layerhaving a first main surface side facing away from a growth substrate anda second main surface side facing the growth substrate; a firstelectrically conductive contact layer arranged on the first main surfaceside; a second electrically conductive contact layer applied to thesecond main surface side; and a holding structure anchored on orpartially in the growth substrate and supporting the functional layerstack with the first electrically conductive contact layer and thesecond electrically conductive contact layer, wherein the holdingstructure extends from the growth substrate along a side portion of thefunctional layer stack to a side portion of the first electricallyconductive contact layer, wherein the holding structure is configured tobe breakable for separating the μ-LED from the holding structure duringa lift-off procedure.
 2. The μ-LED according to claim 1, wherein theactive layer has an increased band gap in edge regions of the μ-LED orin regions which are at least adjacent to the holding structure oradjacent to a break-off edge.
 3. The μ-LED according to claim 1, furthercomprising quantum well intermixing in edge regions of the active layeror in regions of the active layer adjacent to the holding structure oradjacent to a break-off edge.
 4. The μ-LED according claim 1, whereinthe holding structure comprises InGaAlP or AlGaAs or BCB or an oxide ora nitride or a combination of such materials and is electricallynon-conductive.
 5. The μ-LED according to claim 1, wherein the holdingstructure further comprises a layer of InGaAlP or a layer of AlGaAs,wherein the layer of InGaAlP or the layer of AlGaAs is attached to thefunctional layer stack on the first main surface side.
 6. The μ-LEDaccording to claim 1, wherein the holding structure further comprises alayer of InGaAlP or a layer of AlGaAs, and wherein the layer of InGaAlPor the layer of AlGaAs is attached to the functional layer stack on thesecond main surface side and comprises InGaAlP or Al-GaAs.
 7. The μ-LEDaccording to claim 1, wherein the first electrically conductive contactlayer or the second electrically conductive contact layer comprises ITOor ZnO or a metal.